Also consider that Facebook is in a bidding war with Google, MS, and Apple - which has spiked starting salaries in that market.
Maybe west coast candidates won't move but what about all of the people that live in other parts of the country? Most people I know are scrambling to get out of the midwest as fast as they can.
When accounting for these things in a total comp calculation, I do it something like this:
$comp = (1 + 2 + 3 + 4 + 5) - (6 + 7 + 8)
where
[1] Salary / cost of living index for area
[2] adjusted value of health care plan
[3] adjusted expected bonuses/profit sharing
[4] retirement contributions per annum
[5] dollar value of stock options given * chance of options vesting at some worthwhile value (tricky to calculate for startups)
[6] expected hours per week over 40 * .025 * [1]
[7] estimated value of environmental and other stress
[8] cost in time, gas, stress, vehicle wear & tear, inconvenience of commuting
Now, it may well be the case that other companies that you looked at had large negative values of 6 & 7, which makes Fog Creek look great in comparison, but I think that as a profession we're screwing ourselves in the long run if we think about uncompensated overtime as the norm and working normal hours as some sort of bonus :)
If they're exceptional, they can do better - but they'd have to be exceptionally clueless not to be aware of that. I highly doubt any CS student in 2012 is somehow unaware that the market for their skills is sizzling hot at the moment.