That's mostly because in the US they're incumbents, whereas in the UK they're challengers.
Because line sharing and (then) local loop unbundling makes new entries into the market significantly easier (as there isn't the cost to build a whole physical network upfront, and the network can be implemented over time instead) it drives competition in the sky and fees into the ground. It lets challengers challenge, but it's awful for incumbents as they can't just fleece their customers unchallenged.
(As someone who had Internet access in the UK (dialup) for quite a while before moving back to the US, I can tell you that I was surprised at how well it worked and how CHEAP it was. I had Demon and I was amazed at how clueful they were; especially compared to US ISPs.)
But more to the point: the US telecoms are deathly afraid of competition. The same thing goes for the CableCo's. Wireless is killing their wireline business and broadband isn't making up the difference. That's why they are looking at network-neutrality killing services/deals they can monetize. That's not necessarily a bad thing, but when one company essentially OWNS the access loop, it's a recipe for high-prices and bad service to customers.
If our FCC wasn't chock full of industry players looking to land a cushy lobbying spot after their term is up, we'd see a lot more competition (and better options for everyone).
