the other 4/5 are doing just enough to keep their jobs. duh. what's the point in trying if there's really nothing in it for you? everyone knows that if you want a raise, you need to get another job.
That's not necessarily true - I've worked harder on volunteer projects than on fairly well-paying professional jobs.
I think it's more that when there's very little in it for you, your tolerance for bullshit is fairly low. So when there's little bullshit, you keep working hard even if salaries are fairly low. As soon as you start hitting bullshit, you give up and either find a new job or slack off.
This is probably why the study found that the organization has more of an effect on motivation than any personal or work-experience factors - good organizations keep bullshit to a minimum even if they don't pay their people all that much. Like Google.
It also explains why the documentation on nearly every open-source project sucks.
