It's a network operations thing... why should Comcast provide a fat pipe for the rest of the world to benefit from? Just my $.02.
Because their customers PAY them to provide that fat pipe?
You are correct, customers pay Comcast to provide a fat pipe for THEIR use (MSO's typically understand this as eyeball heavy content retrieval, not content generation). They do not provide that pipe for somebody on another network to use, I mean abuse. Comcast's SLA is with their user, not the remote user.
Comcast is cutting off their user's communication session with a remote user. Since every session on a network involves communications between two customers, only one of whom is usually local, this is the same as randomly killing http sessions or IM sessions or disconnecting voice calls.
Also, its a long standing policy on most "broadband" type networks that the do not support user offered services, which this clearly falls into.
I agree that there is a bid truth-in-advertising problem here. Cable providers claim to offer Internet access but instead only deliver a Chinese version of the Internet. If you are not sure why I used the term "Chinese", you should do some research on the Great Firewall of China. Ever since the beginning of the commercial Internet, the killer application has been the same. End users want to communicate with other end users. That is what motivates them to pay a monthly fee to an ISP. Any operational measure that interferes with communication is ultimately non-profitable. Currently, it seems that traffic shaping is the least invasive way of limiting the negative impacts. There clearly is demand for P2P file transfer services and there are hundreds of protocols and protocol variations available to do this. We just need to find the right way that meets the needs of both ISPs and end users. To begin with, it helps if ISPs document the technical reasons why P2P protocols impact their networks negatively. Not all networks are built the same. --Michael Dillon