We're talking about smart people and inevitably they're going to look at friends who've opted for the corporate world and do the math. Certainly as long as the promise of a big payoff is there, then the math might weigh in favor of doing a startup. But it also might not. That whole time value of money thing says that sacrificing income in your twenties is going to hurt you a lot more in the long run than sacrificing income later on.
edit:
Of course, right now the "whole time value of money" is basically negative. ;-)
Coming from a "poor" entrepreneur who has previously held six-figure software engineer salaries, I can say there's more to entrepreneurship than salary. When I busted my ass working overtime to add cool new features, nobody cared. The company doesn't care, the boss doesn't care, your coworkers don't care either. If I have to spend 1/3 of my life at work, I might as well be doing something I love, even if it puts my retirement at risk.
You can retire well even if you only make $10 an hour for 40 years. It just requires you to be very frugal with your expenses and investing wisely. Let interest do the heavy lifting for your retirement :)
The expected value of doing a startup is high -- I think a little higher than being able to guarantee myself $80K/year. If I work on a startup with 1 cofounder for 5 years and it's got a 10% chance of exiting for $10M, my expectation is roughly $100K/year. So if I can afford to take the (rather high) risk of getting nothing, then I should do the startup.
If I value my time differently depending on what I'm working on -- if the startup is lots more fun -- then it's an easy choice.
edit: Of course, right now the "whole time value of money" is basically negative. ;-)