I come from StackOverflow and I see that the answering style here is very different. Even simple yes/no questions get answers with multiple headings and paragraphs.
What happened? Was this a conscious decision? Do I risk being downvoted for short yet complete answers?
One of the reasons that we give and receive verbose answers here is because there is rarely ever 1 correct solution to an RPG problem.
On SO oftentimes an answer can only consist of a small block of code that fixes whatever the problem is. But a good answer will explain it.
But we get two kinds of questions here. The first is a cut and dried rules scenario. Typically this can be answered with a short quotation from a book, or even better an explanation of why or application of how the rule works the way it does.
However, the other type of question we get here is more conceptual. It's sort of the programmers.se or workplace.se type questions. How to handle group dynamics, how to handle specific social situations and how to write adventures/character. These require far more explanation to provide a good answer and are suited for the kind of long answers dealing with multiple facets that places like workplace and programmers were designed for.
Short answers that are complete won't get downvotes, but, depending on how they're written, might not gather upvotes much. Since there are often multiple ways to approach a problem within roleplaying or an RPG's rules, a given answer that says merely "do it this way" rarely feels like a good answer because it doesn't make a case for why the reader should do it that way.
I think you also have to bear in mind that you're comparing a programmer's community to a pen-and-paper community.
First of all, in programming terseness is often appreciated; for example, when looking at bad code, I feel like one of the most common criticisms I hear is "they could have solved that in only one line of code". On the other hand, in pen and paper roleplaying vivid description is appreciated.
Second, your comparing a more professional/functional community to a more hobby/casual community. It's conceivable that on 4:45pm Friday afternoon I'll post a question to StackOverflow which I need answered before I punch out for the weekend. The faster I get my answer and it works, the happier I am as a community member - I might not care about the details. On the other hand, on rpg.stackexchange I doubt anyone logs in while in the middle of a dungeon run with all their buddies sitting around a table waiting for the answer. So I think the very subject matter makes the community less prone to The Fastest Gun and terse answers. People here don't want immediate solutions, they want ideas which they can leverage in games which they are probably going to spend some time preparing for: they're going to draw maps, read rule books and fill out character sheets - maybe even paint some miniatures. When you've already lined up all that work for your game, reading (or writing) an extra 200 words on stackexchange only feels natural.
I've used both a fair bit, so I'll try to add some perspective on the contrast between the sites. First: everything wax eagle said is true about this site.
StackOverflow is fast-paced and not very rewarding. Averaging the scores of all answers in StackOverflow and RPG.SE (and making no attempts to remove outliers), StackOverflow answers net an average 18 reputation whereas RPG.SE ones earn 60 reputation.
At the time of writing, over a count of all answers' scores on Stack Overflow:
Simply put, there's not much incentive to write more than the absolute bare minimum answer on StackOverflow. Questions disappear off the front page in an hour, and everyone is just there to have a highly specific problem fixed that will often be of no use to you. In my experience, putting in any extra effort often goes unrewarded, and there might be only one or two votes given to any answer to the entire question. It's a race to the finish line. So, really, why bother writing more than a line?
Here, meanwhile, things move slower, competition isn't intense, and answers are more rewarding. Furthermore, a particular question is often widely applicable and could be quite interesting to a lot of viewers - and it's going to be there potentially getting their attention for quite a while! You have more time and more incentive to take your time making a good answer - not to mention that good answers often need to explain a lot, as wax eagle pointed out.
On StackOverflow, you often get a code dump and that's it: explanation is often found wanting, and ideas are very regularly not expressed clearly. Sometimes there's simply no motivation to go beyond the code dump (see the above section). Other times, however, this seems like poor communication on behalf of the user: that's as much as they feel it's necessary to express, or as much as they're capable of expressing.
Things don't tend to work that way here. Roleplayers, by the very nature of their hobby, must have pretty good social skills and must be able to communicate and express themselves well. An RPG player who is a terrible communicator is an outlier. Plus, there's rewards aplenty for a half-decent answer, so you can always get some reward for going that extra step or taking a few minutes to improve what you've written.
In IT, though, poor communication and social skills is part of a programmer stereotype that didn't form without substance. Rick Freedman elaborates in this extract from the Communication Skills section of The IT Consultant, a book published in 2000 (emphasis added):
Most IT professionals are intelligent individuals, folks who have mastered a difficult and demanding craft that has required diligent study and training. The idea that they cannot also be trained to communicate well is nonsense. People develop those skills for which they are mentored, compensated, and judged. Superior communication skills have not, until recently, been a requirement of the IT profession. In the mainframe days, IT teams worked in the infamous “glass room,” talking mostly among themselves, usually with a manager from the finance department to act as their interpreter. As computing moved to the desktop, however, and the ability to provide support and service to users in a language they could understand became a valuable skill, communication came to the forefront. Those technicians who could avoid jargon, who could communicate clearly with the secretary, clerk, salesperson, and manager, became valuable commodities. In short, the desktop PC revolution forced IT to become more consultative.
Thankfully, as you can gather from the parts I didn't emphasize, the "glass room" programmers and this stereotype are becoming a thing of the past, and communication skills are becoming increasingly important.
My two copper pieces:
First of all, you have to make your case. You can't just give an answer and hope for the best. If I make a one liner, someone who isn't experienced with that suggestion won't necessarily upvote it. I have to provide a context of how it helped my game or where I saw it used in someone else's game.
Secondly, this site rewards putting more than one answer in each post. When I write five answers into one post, I'll often see comments like "+1 for your second paragraph" indicating that it was a specific suggestion that was worth an upvote. In theory I think it's not supposed to work that way - each answer should be a separate post. But consider which would be more rewarding. If I have 5 suggestions to make and each one earns 2 points, my series of 5 individual suggestions will sit near the bottom for the duration of the thread. If I concatenate them, my long winded suggestion will rise to the top. It's more likely to be accepted that way. It's also more likely to get more upvotes since it's the first thing people will see.
Regarding short answers, no nobody will downvote you for it. You might get comments to expand your answers. The thing I'd worry about is someone else poaching your answer. On several occasions I've posted a couple sentences in response to something. When I've gotten back to checking the site, someone else has paraphrase those sentences in their own post and added a couple paragraphs. I don't begrudge them the karma - they wrote a more complete answer than I did and that should be the accepted answer. But if you're feeling competitive about your answers, putting them out there when they aren't complete isn't going to work in your favor.
