Indeed: perhaps the answer to the symmetry argument is for Netflix clients to just start uploading scads of random data while the movie is streaming. Then the traffic will be "symmetric", although Comcast won't like it after all the last-mile upload links are saturated and customers can't do anything online.
Netflix hasn't done this (and likely won't) because would make it difficult/impossible to control the quality of their service. P2P connections are a bit of a crap-shoot based on things like router configuration, device type and resources. For example, P2P wouldn't work as well on an iPad where you're only caching a few hundred megs of video (and not the whole video) at any given time.
I don't think the parent meant to imply a P2P implementation of Netflix streaming video, just that Netflix is perfectly capable of making that ratio balance out by uploading crap from the clients they have (partial) control over - which would then be traffic coming from Comcast's network.
Torrenting moves large amounts of traffic into last mile infrastructure which tends to already be congested because its very costly to upgrade.
Due to using many distinct flows it also tends to not be very TCP friendly and takes a fairly unequal share of the bandwidth. And while users will give up and do something else when their interactive service becomes slow, a congested torrenting host keeps torrenting.
There doesn't seem to be any congestion on the last mile infrastructure of providers like Comcast. Their problems are all with interconnection to the real internet. It would actually be better for Comcast if their customers were getting more content from eachother over p2p networks than from external providers like Netflix.
