1) It looks good to investors: you've got to believe in it if your worth is in the stock, for instance most of Bill Gates net worth is in Microsoft stock and it would look bad if he sold it all,
2) You pay lower taxes: capital gains vs income, not to mention
3) it sounds good in the press and when people say it
[1]: http://www.sec.gov/Archives/edgar/data/1288776/0001193125060...
I mean, think about it: Mark owns over $10 billion in Facebook stock--he makes over a billion dollars by pushing the stock price up 10% (or loses over a billion if the stock drops 10%). Either way, a $15 million salary would be fairly insignificant...
[1] http://www.businessweek.com/bwdaily/dnflash/content/may2007/...
Can't make people happy.