My brother works long hours on Wall Street. He says that most people in finance retire significantly earlier than the rest of the population. He also says that people working in finance generally value money more than time, and that this is a self-reinforcing system. People not willing to work long hours for a high hourly rate don't find the jobs attractive, and the people already hired prefer not to have extra help; the money to hire each extra person would, essentially, come directly out of their own salaries.

I don't work in finance because I'm currently in university, but I may work in finance after I graduate. I might get a CFA charter and work at a hedge fund. One draw of working in finance is the earning potential. For me, the appeal of a lot of money seems to be three things: I want enough money so that (1) I never have to worry about my own personal financials, (2) I can do a lot of optimal philanthropy, and (3) can fund my intellectual goals, like writing and publishing a book. Those are the top three that come to mind. Given all we know about introspection, it's very unlikely those three are the whole story. But I think it's at least somewhat accurate. Also, as thomblake points out, I can certainly find uses from arbitrarily large amounts of wealth. I suppose there's a theoretical limit at which the marginal utility of an extra dollar is less than the marginal utility of the time I give up to earn it. But I certainly haven't reach it yet. If your friends have, I want to know where they work so I can apply.