I think some tv execs here have trouble coming up with concepts....and they want instant hits. It's probably easier to sell an idea that has been a success elsewhere.
I don't know if British (or other countries') TV is like this, but it seems that here, once you have a hit, there are suddenly six clones of it that spring up on other networks. We have "reality" tv up the yingyang right now (which I'm not a fan of, so I get pretty annoyed lol). They've always done spin-offs of hit shows, but now its almost overboard. There are four variations of Law & Order and three of CSI.
As far as Americanizing a Brit show..??? Who knows. I watch a lot of the British series that they show on PBS here and have no trouble understanding, even though I'm sure I miss the odd joke now and then.