No place is wonderful enough to pay billions of dollars in extra taxes just to live there. If you are a top engineer making $500K/yr, you're only paying ~$65K/yr in CA taxes, and you wouldn't make anywhere close to $500K in other cities. So the decision to live in CA makes perfect financial sense in that scenario. But in the case of a billionaire founder, it simply doesn't make any sense to sell shares while living as a California resident. You're essentially volunteering to pay a ~65% increase in total capital gains taxes over what they would be in a tax-free state.
If Mark has to stay 183 nights in NV (or stay in NV more nights than anywhere else), that might be more of a personal burden and inconvenience than paying CA tax. And if it harms his ability to lead his company, it might ultimately be more expensive as well...
[1] http://www.reuters.com/article/us-usa-campaign-romney-ira-id...