Currently, there's discussion about the question How do the rules that govern a Cleric's Turn Undead ability vary among D&D editions? and concern over its usefulness. We've had other questions like this, for example If I'm invisible do I get a bonus to my saving throws? and What's the history of the Darkness spell?
There's some ongoing complaints in the comments about them, so let's discuss here.
Yes, I believe these are on topic.
Now, Pat calls these out for being "chatty and open-ended." That's clearly the wrong criticism - the answer to the Turn question will be like the one to the Invisible one, which is just "here's the rule in OD/1e/2e/3e/4e/PF". Very cut and dried, and objective. An alternate question like "I want to homebrew my own turn undead system, what should it be like?" would be what would get closed for this reason.
The criticism with more teeth is "but what problem does this solve?" However, I think there's a perfectly good case to be made for knowledge being its own reward here. Questions about how functionality varies by version (e.g. python, IE) abound on the technical SEs. You want to know how it works in different versions so you understand how to use it if you happen to be using that version, or maybe even you're designing your own and want to know the approaches that have already been taken and discarded.
A question like this is objective and on topic; it does have a little bit of the sense of posting a trivia question for the hell of it, but unless someone cranks out 10 of these at a time and is obviously rep-whoring I reckon they're kosher.
I think this is the kind of question that needs to be prefixed with "why do you want to know?"
I mean, they're technically historical in the same vein as "who invented experience points." And they're objective, and so on. But they can also be pretty much just transcribing from a set of rulebooks (general reference), and extremely narrow in general interest.
If someone is looking to move from one edition to another, then they should scope the question to those two editions. Nothing is gained by obfuscating the actual intent of the question, and scoping the question properly improves the odds of generating a solid answer (because answerers need to know a smaller set of editions).
So far as knowledge for the sake of knowledge, compare this question on the Darkness spell to this question on turning undead.
The question on darkness demonstrates research on the part of the questioner, looks at specific aspects of the spell, and probes for reasons behind the design of the darkness spell.
The question on turning undead just asks for a multi-edition rules dump.
So, I would say that "yes, questions about how the rules have changed can be on topic, but no, that question on turning undead is not (or at most is an extremely marginal question)."
