I'm trying to understand what you are saying. I also see holes in some arguments.
1) I agree there's gigantic risk.
If I understood you correctly, you are saying great programmers should have less of the downside of risk with more of its upside.
2) Are you saying great programmers apply to this hot startup in pg's example, pass the interviews, and then refuse the job offer because the compensation offered is too low? If that's what going on, then pg provided something worse than a sketchy anecdote: he lied. He omitted the startup is low-balling candidates it wants to hire. Is this what you are saying?
Or are you saying there are people with the potential of being great programmers who went into other fields because the average compensation of competent (but not great) programmers is low (which may very well be true), and this is the main reason we don't find them?
Also a small correction in "There are any number of people who are capable." It's great programmers we are looking for, not merely capable.
Another in "highly intelligent, incredibly driven people". It's not enough to be highly intelligent and incredibly driven to become a great programmer. You may have aptitude for, but not interest in programming.
3) Is it possible for a great programmer to go into another field? Because if it isn't, maybe the opposite is also true. That you can't take someone from another field and turn them into a great programmer. It's probably as hard for a great programmer to become a great sales person as it is for a great sales person to become a great programmer for example.
4) On the effectiveness of extrinsic motivation of great programmers, we already know extrinsic motivation doesn't work in general. It shouldn't be hard to find research on this. A quick search points to the following. Please correct me if this impression of mine isn't true. I want to find the truth:
http://www.fatih.edu.tr/~hugur/study_hard/Intrinsic%20and%20...
You are suggesting extrinsic motivation of great programmers specifically is an exception.