This is a really interesting observation!
The "American-ness" of the religion, I believe, actually puts UK JW's into a slight state of disequilibrium. The language is quite different, but similar enough that we understand it pretty well. It does however, always have the effect that many witnesses here feel as though they are on slightly foreign ground.
I would never have been converted personally, but my Father was converted over the doorstep, because the American style logic appealed to him. He'd been trained to fly as a bomber pilot by USAAF in Alabama before the US entered into the war, back in 1940. The training methods appealed to him, so when he returned to join the RAF, he was pretty well aux-fait with the American way.
Actually the JW reasoning is quite simplistic, and doesn't sit that easy with Europeans, but my Father loved it. It was this sort of reasoning that got him:
"You can't have a creation without a creator."
"When you buy a new car, you get a maintenence manual with it. The Bible is life's maintenence manual. If you follow it the car / your life will run well."
"Obviously Jehovah's organisation is based in the US. It's the biggest country in the World, so that's where Jehovah bases it."
He had dozens of similar sayings, which, whilst they satisfied me as a child, did not reach my heart in the same way that it reached his. So I left!
Englishman.