Talk to some serial entrepreneurs. Many of them are already rich, and don't need to work, but they do it anyway. They're motivated by the challenge, not the money.
"Many of them are already rich" -- I think lots of behaviors change once someone is rich. You can choose what to work on, you can walk away from bad situations. I dont think the behaviors of the rich apply to the non-rich.
Well, are they working for themselves or for someone else? That has to come into play regarding motivation.
I'm sure, but the money definitely helps. If only because it enables them to do what they do.