I'm not counting angel rounds as a series A here. I'm talking about the big rounds that are invested to scale the business of an already-successful product. Companies that take these kinds of rounds can still fail, but the rate is nowhere near the same as for an early stage startup. And there's still upside in it for the employees: if you get .01% at a $100M series B valuation, and the company eventually IPOs for $1B, you've walked away with a grant worth $100,000.
We're only a factor of ~4 apart -- make that .02% and a $2B exit (or .01% at 50M for a $2B exit, or...), and you're basically there. And we haven't even talked about raises and/or retention grants, yet. So perhaps "certainly" was a strong choice of words, but it isn't totally ridiculous, either. Being a later stage employee at a hot company is a pretty good deal.