Sure, the risk is higher. But so is the potential reward. And that shouldn't go unnoticed.
As the original poster points out, if you're not in the first few employees, the potential reward is smaller than what you'd make at a big company.
Despite popular opinion, risk and reward are not cosmically related.
They mean the risk is higher quantitatively because the money you're giving up from Google, etc. is higher than average for a software engineer. OTOH, nothing about the reward changes depending on what other places you could be working at.