Bike porn

Pretty sure Campagnolo trademarked the term Campy a long time ago... And they seem to be happy using it for the Campy Tech Lab™.

Argument over stocking parts applies to all high end kit anywhere. Likelihood of average bike shop having niche carbon wheel spoke to hand or cartridge bearings for your headset is slim if you live outside major cities. Internet makes it a non issue. I live in reach of a number of shops that stock parts but I still keep a spare set of shift cables and other wear items.

In summary people just pick the group they like and can afford... Sod patriotism or we would all be on sturmey and stuck in one gear.

I'm guessing it's 'cause 'Mericans like it all matchy-matchy and SRAM make better-looking levers and chainsets than Shimano.
They're also fans of abbreviation, so one double-tap lever is 'superior to' two single-tap levers.
In all seriousness though, it's because Cam-pan-yolo isn't a serious alternative to Shimano in America. With Campag (yes, Campag, not fucking 'Campy') you're talking a week's wait for your bike shop to get the right shifter cable in stock, versus SRAM-Shimano harmony and everything available right away.
The American guy who rides Campag has two other Campag-equipped bikes of equal specification to the one he just broke, basically.