Well, US banks aren't. Dutch banks are doing it just fine:
Works very well and I trust this method a lot more than a payment processor that's not my bank.
I'm not entirely sure what the rules are from the merchant's side, however.
Point being: The precedent of putting Paypal under the behemoth of banking laws/PCI/Frank-Dodd is more frightening than people still willing to do business with them getting shafted. Dare I say, if it were easier and less regulated to move money through the interwebs, Paypal wouldn't be an issue.