It does at least raise the bar on how much you need to make from an account before it gets shut down. If each account was making $50 before getting canned then it wouldn't make sense at $99/account.
This of course assumes they aren't just stealing credit card numbers and using those to sign up. In that case the higher account price is not much of a barrier.
Another way to look at this is Google made $2.4M off of these spammer accounts. Not a lot for a Google sized company, but it's still not nothing.
