It's a conscious trade-off. One fear is that having comments that are edited after the discussion has taken place will reduce the utility of the future archive. There is also the hope that the current window-of-edit policy encourages people to do a better job the first time while still allowing them to catch silly errors.

I'm pretty sure that if you ask nicely by email that you can find an admin who will remove your email for you. Just wondering --- is there a reason you feel you have to remove it at this point?

Well the reason is that it shows up in google when searching for my name and I'd rather not have my e-mail widely available like that, especially for spammers. Thanks for the tip I'll ask the admins!