Paid holiday entitlement in the UK and USA?

I understand that Americans get only one or two weeks' paid leave per year, even if they are in quite senior positions. Here in the UK 4 weeks is standard, more as you move into more senior positions. I wondered how historically it had come about that Americans get such little time off work, how they feel about it and how it works in practice - do they actually only go away for one week a year or do they have some unofficial way of getting a decent break from work?