I agree PAXboy - the first couple of reasons are for sure something to do with it. They have lowered expectations so much as an industry that now Americans travelling domestically don't know what it is like travelling in other parts of the world.
It could also be that the Americans were doing it for so much longer than everyone else - there was no train system to compete with such as in Europe, that flying became less of a "luxury" sooner.
Speaking to an American friend yesterday, she says that although in competitive situations such as retail and the restaurant industry the customer service levels are high, public services in the US have notoriously low levels, and the airlines, through all the mergers and consolidation that has been going on, now often see themselves as a public service and have correspondingly low levels of customer care.
The real kicker in my mind is the code share - KLM and Northwest used to have an almost synchronised product. Now if I book BA and get AA I have a completely different experience. Should be flying AA to the US in November so I will muse about it until then!
XSB