1080p, not so much... that's more reserved for On-Demand and Pay-Per-View. For normal broadcast/cable viewing, it's usually 720p or 1080i (which are also considered HD).

Again, I haven't had Comcast in years, so whether you have to pay for it or not, I have no idea.

But I did find this wiki link that shows what each network (in the USA) broadcasts in, and other details:

https://en.wikipedia.org/wiki/High-definition_television_in_the_United_States