If i want to edit a typo, now i just can't because of this limit.
So what is the reason for this limit? And what is the way to correct typo, do i really need to do any more editing if all i want to do is change 2 letters order?
If it's only one typo, should you really be editing the post?
Sometimes the answer is yes, and we trust users with 1000 reputation to make that distinction.
For users with less rep, and in general, we prefer substantial edits. Improve grammar, spelling, and clarity; when needed, edit in info from the poster's comments. And so on.
Note that you can always edit your own posts.
For more information, see How to overcome "Edits must be at least 6 characters"?