It's a smart move to offer a backup tool, especially when enforcing a TOS that's subject to interpretation and causes (alleged) violators to complain very loudly in public forums when their accounts are permanently canceled and their data becomes inaccessible. They'll get less sympathy this way ("You backed up your data, didn't you?"), although the most important thing here is that all users are given a chance to feel that they own their own data. That's more than a mere PR move, it's a perceived right.