It's not bad etiquette at all.
By posting a question, the questioner should take the time to clearly write what the problem is, what they've tried, show the relevant code, and what they want the result to be. And to do it in the best spelling and grammar possible. Yes, we obviously have to take into account non-native English speakers, and be more lenient with them.
Many posters have over 5,000 votes, and many more have over 1,000 votes.. It's not realistic to go back to the votes or even be notified every time someone makes an edit. Usually low quality questions also have spelling errors that get edited. Posts can also be edited an UNLIMITED number of times.
It's not realistic to even have a system that notifies you of every edit on a question or answer you previously down voted.
Like Rosenate said, usually if they edit their question and it's a lot better, someone else will upvote them. 1 upvote = 2.5 downvotes on questions. 1 upvote = 5 downvotes on answers.
The system already works great. People should get downvoted that write terrible quality posts the first time. That will help them learn how to take more time and effort into writing their future posts.