[rayiner]

For your hypothetical to hold, you’d expect to see some providers with near 100% market share. (You’d also have to assume Comcast builds and maintains infrastructure to millions of households in areas where it has no market share.) Who are they? FiOS’s market share is 40% in its footprint. AT&T’s fiber is around 25% now, hoping to reach 50% by 2023.

The only other way to get your math to work out is to assume that only a very small portion of Comcast’s footprint has no other cable/fiber competitor.

As to your cell situation—what mechanism do you think creates this competition-limiting monopoly? And why doesn’t that same mechanism apply to say my house (in the DC exurbs), where all of the big 4 have a decent signal? (Or the majority of the country, where at least three providers have coverage?)