I'm not paid to listen to music I like but I might need to be paid to listen to music you like. Same deal with browsing your websites, reading your books and watching your movies.

Well, but the fact that it's the music I choose to listen to etc. means it doesn't drain my willpower as much. See also this.

If you're enjoying your work and having your cached selves do most of it,

Actually I meant the part of that post where if you pay someone to do something they'll enjoy doing it less.

what's the big deal with long hours?

Less time left to do the other things I mentioned? Certain things are terminal values; fiat currency isn't one of those. (Granted, I don't only do my current job for the cash, but I wouldn't spend as much time on it if I didn't need money.)