Let's just cut through the BS
I think the reason we're having such a lively discussion is we're looking for a distinction that doesn't exist.
Here's the gist of it all. Comcast and other ISP's that have caps are doing it for one reason and one reason alone: to protect their business interests. Simple as that. Comcast has been in the business of selling TV. Well, then along came Netflix, Roku, Amazon Video, and others, and these products undercut their revenue, so they have to find a way to rein them in, and caps are really the second-best way. The best way, of course, would be to simply block them, but that would be politically unwise in the extreme. Now we see this new service using the 360, and, wonder of wonders, it isn't capped. Why not? We can spend all day trying to figure it out, but the answer is right there: Comcast is making money off of it, so it's to their advantage if people use it.
If Comcast or any other cable company was really facing a last-mile bandwidth crunch, there's an easy way to fix that: delete cable channels. And before anyone says there's nothing to delete, sure there is. Just about every cable channel now has an SD and HD version. There's no reason the SD channels can't be dropped, since it's entirely possible to downconvert the HD signal for a standard TV. I'm not saying it's as easy as flipping a switch, but it could be done, and that would free up bandwidth for Internet.
But, in the end, this incident simply proves that this is all about the fact that Comcast is looking to monetize that data, one way or another. They aren't content to simply sell you access; they also want those bits to also make them money, either through a data cap or through a partnership with another company.
If Comcast, AT&T, and TWC were airlines, they'd sell you a ticket, then charge you extra for the seat.