That doesn't discount the fact that laying cable costs lots of money is a natural monopoly.
Wait, so in one post, you challenge HN's readership to prove that Comcast is a monopoly, and then two posts later you assert that cable is a natural monopoly. I'm confused what point you're trying to make.
Comcast is a natural monopoly, and there isn't anything wrong with that. Competitors are free right now to lay cabling to areas where Comcast already serves, they just choose not to because it isn't a smart financial decision.