Not true. Google Groups had the ability to 'delete' messages. I put the word delete in quotes because it was more of a hide from other GG users delete and not a true delete. On Usenet those messages were still visible to everyone as it propagated the thread to every NNTP server around the world.

I vote for a short (1-4 hour) edit limit. This is mostly because I'm a bad at spelling, grammar and punctuation. I usually have to go back and correct. Or, maybe after reading, my post is a babbling pile of incoherent trash. That gives me a chance to immediately go back and correct it. After that though, any changes must be done through another posting.