I'm not sure that's true: While the US is an extremely large market, it isn't the leading cellphone market by a long shot. Asia, Europe and Japan are where most mobiles are sold and where the most innovative designs are introduced.
Look at the iphone for example: It's influence was almost ENTIRELY restricted to the North American market. Even after it was jailbroken and leaked out of the US, it has not captured the market.

I believe the iPhone's major problem was Apple's exclusive tie up with ATT. Add to that: the requirement of iTunes, the walled garden nature of the device, the unremovable battery, the "you're holding it wrong" attitude and the general childishness of it's userbase, the legal restrictiveness of the iPhones SDK ... I could go on and on.

All this makes me NOT want to touch it even with a ten foot long pole.
YMMV.

Edit: I almost forgot Steve Jobs and his marketing folk: The reality distortion field is awe inspiring. I wish Nokia had that.