Well, for British people at least, the American accent is just a matter of getting English wrong. Americans have to learn to speak the language properly in order to do our accent!
Joking aside, it probably is because we hear American accents via TV and films far more often than the average American hears an English or Australian accent. In fact, I knew a couple of people at school who (whilst brought up in the UK) had spent most of their younger years watching American TV rather than socialising, and thus had a tendency to use American slang and words, such as faucet.