How much did Netflix's Cogent bill go down? How much of the "work" that Cogent was doing is Netflix now doing themselves? How many hops of the traceroute are owned by Netflix, and how many hops by Comcast?
When I rent a rack in One Wilshire in LA, CA, it comes with power, cooling, and a network link. When I pay let's say $1000/mo for that 1Gbps link, it's not just the link from my rack to their router that I'm paying for. And when I send 1Gbps of packets up through that link, it's not just CoreSite at One Wilshire carrying the cost of delivering those packets.
At some point, yes, I do expect Comcast to get their "fair share" of that $1k/mo. If Comcast is PAID zero dollars for delivering that 1Gbps, then I want this free bandwidth gravy train to propagate all the way back to me. Comcast, please sign me up for 10 of those free 10Gbe links you're giving out, ok? Just tell me where to rent space where I can get those free 10Gbe cross connects to your network.
But then, you can also flip the perspective and ask the question, why doesn't Comcast have to pay for all their bandwidth? Shouldn't they be paying $1,000/mo for their Gbe's?
So why does bandwidth cost money, or more specifically when should bandwidth cost money? Price, as always, is just a means of efficiently allocating scarce resources. Price can only possibly be zero if there is no scarcity. Is it possible there's no scarcity of bandwidth on Comcast's network? Now that would be comical!
I think the answer lies partially in another development. Ask Netflix to chart the cost in terms of Watts and Rack Units to deliver 1Gbps of video streams. My theory would be the cost in terms of space and electricity to generate 10Gbe of video streams has dropped orders of magnitude. This means bandwidth will be an increasing portion of your bill no matter what. It also puts more pressure on scarcity of bandwidth when the ease of which you can generate 10Gbps of useful traffic is down to just a few servers.