Geez. Hard to believe that SFO experience trumps making $70K/yr in a middle-tier city, living in your own house and paying less for its mortgage.
At $70k a year, you should take home roughly $70k / 12 * 0.65 = $3.8k each month.
At $120k a year (rough estimate for a Facebook engineer, so correct me if this part is unrealistic), you should take home roughly $120k / 12 * 0.65 = $6.5k each month. If you're paying $3k each month on rent (which is quite generous if you're living by yourself), that leaves you with $3.5k each month.
That means that your $70k job only leaves you $300 a month for rent, in order to have the same amount of money left over. That's really pushing it, considering it's only half of the median USA apartment rental, and considering I paid $400 a month for a modest apartment 4 years ago in Springfield, MO, which as I understand it is in one of the cheapest areas in the country.
Obviously there are other effects here that I'm missing. My 65% take home portion could be completely wrong. Food prices are almost surely higher in SF (of course, most startups and tech companies provide some free meals).
Having lots of space is obviously a major difference, but is very subjective. Many people who live in a city probably wouldn't want to maintain a yard or a larger house or need to drive everywhere. I definitely prefer the space.