I wonder "how much" and "what" taxes are on Stock awards vs if it was given in a normal salary. I'm betting there is a tax savings in stock awards.
The stock awards that Mr. Cook gets are, for tax purposes, treated pretty much the same as ordinary income. He owes taxes on them based on their value when they vest as if he received that same amount in cash. If he chooses to keep them past that point, then any gains (or losses) he realizes are, for tax purposes, treated as capital gains (or losses). It's the same as if he were paid in cash and used it to purchase shares.
When Mr. Cook's shares vest, whether he sells any at the time or not, Apple typically withholds more than 50% of those shares to meet tax withholding requirements.
The reason - or one important reason - for compensating executives through equity awards rather than salary is to more closely align their interests with those of shareholders.