Disclaimer, I am both European and American, so I am not taking any side, just feel I have a good grip on this
- Mentality: An "average US person" values a good or service based on needs and desires. An "average European person" values a good or service based on what it should cost, based on component costs, etc... It is very hard for a European person to feel good about purchasing an iPhone, when an Android phone with a better spec sheet sells for cheaper. A US person would say "who cares, if it feels better, I am willing to pay a premium", when the Euro person would think "I can have NFC on Android and pay less".
A Euro person would get as much satisfaction (if not more) in the actual deal than they're getting, as in the device they're getting.
Apple makes high profit margin, euro people can't stand that, US people don't care.
- US company: obviously buying American is a plus for US people, and is probably a minus for many Europeans.
- affordability: US people have more buying power
- iPhone is much better in US: Siri actually works and is of value, Maps is decent... Those were some the biggest selling points of the iPhone 4S and 5, and they just don't perform well in EU. Not clear if iTunes Radio is coming outside US or not, but that could be one more to the list.