Thus, my risk is much lower than a founder's.
Your expected opportunity cost in the case of failure is smaller--like you say, you draw salary as soon as you start (though the salary is often less than market rate). I will point out that employees are usually less well-informed than founders about a company tanking, so will usually have a couple of months lag in looking for another job, and that "I was employee 3 at Vunge Games" doesn't sound nearly as good as "I founded Vunge Games" when you're at interviews.
Your expected payoff in the case of success is probably at least an order of magnitude smaller, and from anecdotal evidence seems to not be much more than it takes to make up the market wage shortfall over the course of your employment.
This isn't intended to be pedantry--I figure that all of them (but especially the expected opportunity cost) are likely to vary based on region and are worth noting as hidden costs. But from my perspective, being an early employee at a start-up is a bit of a mug's game when the alternative is bootstrapped founding from corporate employment.