It's a fools errand to try to prevent people from creating anonymous accounts using something like a throw-away email address. It's just far to easy to do.
I think they just want to make it as hard as possible to prevent as much bot script account creation as they can.
That's a good point, but it doesn't explain why they prevent you from typing "mallinator.com" into a post. To me that's taking it a bit too far -- bots don't read other posts.
Probably because they have the one filtering engine across their entire estate.