Most of your cable service's video is actually delivered over IP, but it is on dedicated RF spectrum, even though it's on the same physical wire. If Comcast wants to deliver video to my STB over separate channels, I don't care what protocol they decide to use.

However, if they're delivering video to a generalized computing device in my home, over my home Ethernet network, over the same downstream channels as Internet traffic, and further, they're prioritizing that traffic, that's different. If there was congestion in the last mile that wasn't just me hitting my rate limit with synthetic traffic, Comcast's traffic would be prioritized, and that's not right. It would be affecting your internet bandwidth. If Comcast had provisioned dedicated RF channels for handling this traffic, just as they do for your STB, then I could at least see your point, but that's just not the case.

[edit: typo]