Here is my speculation.
ISP pay each other if/when they enter private peering agreements. And the terms involving how much traffic you are sending out of your network to other networks. So in the past Comcast was making out like a bandit, they charge the user for Internet, the user downloads a lot and didn't send a lot, hence the asynchrous rates (huge download/small upload). And they get money from the ISP's to get their traffic to the comcast eyeballs (users on the end of a cable modem).
Now enter bit torrent, suddenly users are sending out data, at a slower rate mind you, but we all know these bits add up when your bitorrent client is an icon in the taskbar steadily uploading 384kbits second.
Suddenly Comcasts ratio of traffic with peers is changing and it's not making money hand over fist anymore. And it has to increase it's bandwidth rates in competition with other services like FIOS, which is getting pretty popular in the DC metro area (my home).