I think your last sentence "and recognize a boo-boo, it would be nice to be able to correct my mistake to avoid a permanent record of my foolishness"

How can you make a mistake in a comment? If you don't mean what you write don't post it... And don't worry about people calling you foolish (I am sure there is a famous quote for that to put it more eloquently).

Also, note that there is no post preview when you submit so being able to modify after you post fills that functionality gap.