Part of it in the US is that a lot of corps are scaling back so remaining employees are expected to pick up the slack, hence in some cases long hours during the week and/or weekend to stay even w/ projects. And with the economy heading for a recession & people also needing health care benefits that come w/ their jobs, they feel the need to put in those type of hours to keep their jobs.
I also joke that we got screwed when the Puritans came over on the Mayblower - or, as a UK friend said to me once, 1week's vacation for a whole year's work?

Over here vacation times are a lot less than in UK/Europe. Usually most people starting with a company get 1-2weeks, and have to work up to 3-4weeks (usually after being with a company for a # of years). I decided I'm going to start taking the US official bank holidays & maybe toss in the UK ones as well since I have UK clients
I work out of home so it's easy to slip into the working late or on weekends, but I'm trying to be better about it. Now, if I'm on the laptop on the weekend (checking FT for example) and a biz email is in my inbox I won't read it until Monday morning. I also shut off the biz line phone ringer & close the door after 5-6pm. Having said that, I also deal w/ Asia as well as Europe and being based in LA, the dif time zones can make some long hours. But I really try to get my int'l clients/contacts to contact me in the few hours we overlap so I don't have to stay in the office in the evening.
And of course there's the bit about blowing off in the week when I should be working so then I say I'll catch up on the weekend, but then on the weekend I don't feel like it cuz hey - it's the weekend. Oops. In that case some long hours during the week are self-induced. Knock self upside head LOL.
Cheers.