There's a great deal of risk and uncertainty involved in foregoing the completion of a degree, a potentially-salaried position at a stable firm, and so forth in favor of starting a company that is statistically unlikely to succeed.
The fact that the risk wasn't called in, so to speak -- that the worst case scenarios did not come to pass -- in no way diminishes what was risked. Beside, you have cherry-picked two cases where it is quite easy to construct a plausible a sounding (and factually false) "no risk" argument. HN routinely features entrepreneurship efforts where much was gained and much was won. Your main gripe appears to be that the risk-reward maxim is not describing a literal, linear relationship.
Next up, the sun doesn't always set in the west! (provided certain map orientations, times of the year and fluctuations in magnetic north)