I would be quite happy for someone to correct a minor spelling error in an answer (or question) that I posted. Would that offend some people? Or is there another reason that it is not allowed? This restriction makes sense on the other stackexchange sites but here it is a different situation because English learners who come here should be able to expect that examples and definitions are correctly spelled.
Is the post otherwise so perfect that it cannot be improved in any other way?
Somehow, I doubt that. :)
The reason for the restriction is that suggested edits are peer approved; they take time and effort for your fellow users to read and process. That is why we ask that your edit suggestions please be substantive improvements, at least 6 characters' worth. I do not feel this is an onerous requirement.
And if you do, then earn 2k rep at which point you can make all the 1 character edits your heart desires.
Another factor is that after some number of edits a post (question or answer) automatically kicks over to community wiki, which means (as I understand it) the previous owner loses any rep that was there and loses the ability to gain more. So you should try to consolidate edits -- one edit fixing six one-character errors is better than six separate edits (even if they were possible).
@Jeff's answer is fair enough, what I think the problem resides in is that people without enough reputation to make small edits without approval are still presented with the message ... unless absolutely necessary giving them the illusion that they still can make that minor edits if just they can play the absolutely necessary card, but that's not possible at all. It's just misleading.
If low reputation users should wait for approval of any >6 char edit anyway, why not allow them to make any minor edit and still have to wait for approval?
I realize this would make the stack of approval-pending edits bigger for other users to consume, this minor edits could have a somewhat lower priority, so more elaborate edits still get resolved sooner.