We don't need an "edited" tab. This would be difficult to implement. Furthermore, in order to be useful, each edited list would need to be customized for each user, which again would be difficult to develop and maintain in a manner that keeps the system light and fast.
Instead, we just need to find better techniques for managing our voting.
I generally hold off on my downvotes in the first 10 minutes after an answer is posted. There have been many occasions where I've written an answer, posted it, reviewed it, and then edited it again to fix a mistake, flaw, or logical error that I missed while composing the post.
Thus, during the first 10 minutes of the post, it's likely that it's in a state of flux, especially considering there's a 5 minute window on edits before further edits increment the revision history.
The situations you describe don't happen on posts that are older, as there's no longer any activity or life to breathe into those threads.
Of course, I don't generally lead with downvotes either. I lead with comments. If someone posts something that may be incorrect but can be fixed, then I simply point out the problem. Anyone who is really here to help would likely edit and fix the problem, making the post upvote-worthy and also creating yet another example to show why Stack Overflow is awesome.
If the content is dangerously incorrect, something that must be pointed out right away, then I'll lead with a downvote followed by a comment. Or if the person refuses to fix the problem, then I'll add a downvote. However, I don't use my downvotes for trivial matters until I'm sure the problem is not likely to be fixed.
Lastly, it's worth pointing out that many times when I've left a comment, I'll get a ping 20 to 30 minutes later thanking me and explaining that the problem is fixed. This prompts me to review the post and change my vote, if warranted.
Now, I realize many people are concerned about backlash from someone whose post they've downvoted. In my experience, it's not the downvote that sets people off; instead, it's how we word our feedback:
While this type of unconstructive comment is more punitive:
-1 for using eval in your code and making it less secure.
This type of comment is more constructive and motivating:
Hi Bob, I noticed you used eval in your solution. eval is very dangerous because it's subject to man-in-the-middle attacks. You should instead use an anonymous function, which would prevent that from being a problem and also make your answer awesome!
I stopped getting serially downvoted by angry, pitchfork-wielding users once I stopped leaving comments in the first format, and I leave the door open for people to ask me to review their changes if they want, which gives me an opportunity to change my vote on content that has changed.
In short, we don't need an "edited" tab, we just need to find better ways to manage our votes.