The real answer from an Ex-Employee...
I used to work for Comcast so I know this as fact.
Comcast, represented as one company is actually two entities.
Comcast Media is the second entity. The fact that help proves this is the stock symbols, there are two. Now companies including comcast get their media (video as a example) from Comcast media. Directv does it. Charter does it. Even Hulu does it.
Comcast does not have to give Comcast media priority over it's network because the traffic never leaves their network. I can't recall where Comcast Media is located but Comcast does have a backbone running between cities and Comcast Media is on the backbone. With Comcast Media being on the network and the traffic never having to leave the network to get to a subscriber, the bandwidth will appear to come as priority but all it is that the data does not have to touch the latency side of the internet.
Comcast does the same thing with the phone service. The phone service is on a different QAM channel that come to the house. When you call someone within the Comcast network, the phone call never leaves the network thereby the call looking like it gets priority.
The same as with any digital phone service from cable providers. They NEVER touch the PSTN until it reaches a customer outside of that network.
And if they wanted to get even braver they could count Sprint customers as being free calls even if they were LD due to TWC and others using Sprint as their wholesale provider.