Update Dec. 25, 2013. I should make explicit that I'm referring to edits that are based on the existing question and answer. Viz I'm referring to edits discussed at Clarify an old answer. I agree with Asaf that not every edit should be added to a question.
I just ran into this problem myself. At first, I thought about editing to add my questions. Then I read Clarify an old answer. This was never a duplicate asks different things. Bill Dubuque explained it perfectly. Asaf Karaglia is right about citing previous questions. I'm sorry I forgot hence I just added the reference. I didn't forget it for this.
Unfortunately, This was never a duplicate was closed quickly. Hence are there benefits and pros to edits based on the existing question and answer? Can you talk about them please? So far I came across these.
It would save a lot of hassle, time, and trouble that all users have to suffer through when a question is wrongly closed. Bill Dubuque had to write his paragraph and I'm waiting for votes.
Reading the old and new posts would be a lot easier. When new questions are posted separately, you'd have to keep on flipping between the websites. Even then it is hard to compare both pages because of the constant opening and closing. This is awfully inconvenient.
If a question like mine that is not a duplicate can get closed this quickly, what about questions like the one you linked to? Then we are just back at point 1 and have to pain through the fuss.
It is more convenient to combine and keep similar things in one page. Like Trevor Alexander says in http://meta.math.stackexchange.com/a/4110/53934,
More questions is more search results, which need to be human-parseable. More answers is more knowledge in a convenient place.
Bill Dubuque talks more about this at http://meta.math.stackexchange.com/a/4110/53934.
Gerry Myerson wrote at http://meta.math.stackexchange.com/questions/4108/clarify-an-old-answer
A comment will not bump an old question to the front page and probably won't be seen by anyone except the person whose question or answer receives the comment. Yelling at people for bumping old questions is reserved for those who bump by making trivial edits; substantive edits shouldn't upset anyone.