From the aforementioned NY Times story:
Health is the most private of all matters for very good reason, and the Securities and Exchange Commission has never disciplined a company for a failure to disclose health problems. In part, we all buy, sell and trade on someone’s health without knowing their fates. Sergey Brin or Larry Page, Google’s founders, may be fit as fiddles, but they could get run over tomorrow by a Prius in Palo Alto (a Prius would still hurt, right?).