I can remember some CEOs who works for a symbolic $1/year (http://en.wikipedia.org/wiki/One-dollar_salary). They certainly do it because they like what they do, not because they have unpaid bills.

I still posit that most people who "go to work" consider monetary or other material reward their work provides very important. Many of them would trade their current place of employment to another comparable place that would pay, say, 30% more. This probably does not matter when you earn $100k+, but most people don't.

What is true from my experience is that paying more does not increase motivation when autonomy, mastery, and purpose are addressed poorly. It just feels like a more fair compensation for the pain of working in such an environment.