Well, as evidence that they're trying to cut down on "hacking" the box, I submit an excerpt from a comment on the ReplayTV section of AVS Forum:

"I received a 4504 Monday because I waited too long to order the 4040 and they ran out of stock (wasn't available on Amazon for weeks either). Neither ReplayPC or SwapDV works on the 4504-- so folks should be aware that when SB does the firmware upgrade making the 4000 series equivalent to the 4500 series, the usual apps for transfer will not work until the great gods of video do necessary patches to make them run again. Translated, I would have everything across to your PC that you want to have there as your unit could get pretty congested for a bit depending on how difficult the work around is. Selfishly, I am glad we will all be in the same boat as was bummed that I didn't order sooner and get a 4040. "

So it looks like this isn't just a token "cover your ass" move, they're really trying to stop people from hacking the boxen.

Tivo's looking better every day.