Actually, you are wrong. FB is doing a 3-1 stock split, but the newly issued shares don't have voting rights. So, in your case, Mark would own 225 shares, but only 75 of those would have voting rights, and 150 would be non-voting. Thus, he could sell the 150 non-voting shares and still retain the same percentage of voting control despite only having 1/3 of the "income" rights.
"Income" that won't be distributed as dividend until he decides so. When he needs some cash he might prefer to increase the CEO compensation package instead. Why share the profits with the rest of the owners?
1. Legally, Zuckerberg still bears fiduciary responsibility for all shareholders. If he decided to pay himself all the profits as CEO, he would get sued, and lose.
2. Almost all of Zuckerberg's wealth is tied up in his FB shares. If he starts acting in a way such that other investors don't believe he will support their interests, the value of those shares will go down. It would hurt Zuckerberg a lot more than anyone else.
He can't give himself all the profits, but he can easily raise his compensation from $5mn to $50mn without raising an eyebrow. He can also untie his wealth from fb shares while keeping control, as we have seen.
(Actually it seems the $5mn are security expenses and use of corporate planes... It seems he doesn't really get any compensation beyond the $1 salary? Poor boy...)
