(Non-D&D answer since this question is no longer D&D5-tagged.)
I think we've hit a point where different game systems have different standards and your answer should reflect that.
- Modern D&D has a lot of rules, written by multiple authors, which accumulate over time.
- There are official channels for rules updates and clarifications, which also accumulate over time.
- The D&D rules interact with each other in complex ways.
- The D&D community in online fora &c. has specific concepts like "rules as written," which constitute guidelines for how a game text should be interpreted and also for how your analysis should be presented.
- AFAIK, they still do the thing where you can ask a paid customer service representative your game specific question.
So D&D5 answers should be written with all this in mind.
Non-D&D answers should be written with the specific game's specific circumstances in mind:
- How was this specific game text intended to be read and used?
- How are this game's "canonical" or "official" clarifications normally communicated?
- How "technical" is the terminology in the text?
Consider this example doppelgreener offered in the comments:
As a high-profile alternative example, the Fate community utilises developer commentary heavily to the point that our community's go-to third party Fate SRD incorporates a lot of it as sidebars—it's readily available, highly dependable, and super relevant guidance on how to best utilise the system's elements.
So, there's no one-size-fits-all "policy" shortcut here, you need to know how a particular game and community operate. (In WotC's case they do straight-up tell you what's "official," as Purple Monkey pointed out in the comments.)