I think it's part of the Credit Card Accountability, Responsibility and Disclosure (CARD) -- the new laws that were passed.

They have to send out your bill no later than 21 days before it's due. No more of this 20 days from when the statement is cut, but it takes a couple days to print and mail, so there's really not that much time left.

Of course Chase is doing it now before it kicks in and making it sound like they're being nice.