Easy answer? Low population density, lots of space, relative to Europe (totally unfamiliar with Beijing). UW (U district) is a bit cheaper than capital hill (when I lived in U district, 1 parking spot came w/ rent, an additional spot was $50/mo).
It is true that the US has lots of space, but the cost of driving (and parking) is still ridiculously low compared to other countries with similar characteristics (Canada/Australia)...and people still complain about it being too expensive (god, $4/gallon gas, outrage!).