Antagonistic questions all around
Everybody is concerned with "is it right", "it isn't right", getting the service paid for, mitigating customers using more than their fair share, etc. Why don't they work together?
Say Comcast finds and hires two developers of BitTorrent apps. I'd hope Azureus is one, but uTorrent is #1, I think. In order to work together, a Torrent client needs to detect where the network is "free" and where it hurts the ISP more. If my neighbor and I are using the same Torrent, we should have all caps removed and be screaming data at each other (dare I suggest a DOCSIS tier for caps within a neighborhood? very far out thinking). Maybe traffic within an ISP, but outside of a city has a higher cost, maybe connections that leave the ISP altogether cost ten times as much as that. This is known as tiered Torrents. I've lost the paper that documented it, but it's been implemented in the academic world for study, but I've not seen it released to the public.
Simplest, a torrent client could traceroute every new peer. Peers within the first "hop" or two have a cost of 0-0.5 (or something very low), peers a few hops away may be 1-5, peers that leave the ISP are 10. Heck, maybe each hop increases "cost" exponentially. Currently, the only factor that matters is how much clients share. We're not talking about a cost in dollars for the customer, by the way, we're talking about a cost against a weighted connection table for potential clients. Clients will be more "hesitant" to connect to clients far away, but will not necessarily refuse to do so. If there are 100 suitable peers, and we wish to connect to 50, you start with the list earlier in your traceroute, and everyone on the other side of your ISP is the same.
Everybody wins in this scenario. The network is more efficient, the ISP pays less. The user doesn't care, except that they get easier access to clients that aren't throttled. The ISP's biggest worry is the bandwidth that goes to another ISP -- if they can keep that constrained while the customers still get their data, everybody wins. Very popular torrents will likely be able to find a hand full of seeds within one large ISP.
The downside, aside from programming complexity, is that there are some fat servers out there that will now "cost more" and the maximum download may go down because you don't connect to them. But, if it keeps your ISP from throttling so much, even that may be a win.