The rationale for the 10 minute edit window was this: You don’t want people to ask a question, then, upon seeing that the answers coming in aren’t taking the direction that the asker intended, go back and tweak the question to get the kind of answers they want. The problem with that, of course, is that the first few answers then look like the respondents didn’t read the question carefully, when it was actually the question that shifted. Even posting a revision marked “Edited” still leaves those first responses dangling awkwardly. In those situations, it’s better for the asker to own the mistake and post an in-thread comment redirecting the question. That way, the coherency of the thread is preserved.
We mods regularly get requests from users who don’t like the direction their thread has taken asking us to send the Q back to them for editing, and we regularly decline to do this if we suspect that this will trash the work of people who answered in good faith. If we open a big editing window, then we’re basically removing that safeguard of mod review.
Yeah, there’s the problem of typos, broken links, etc., but frankly, that’s all quite avoidable with a bit of proofreading, and you can always flag your own question if you miss the editing window.