Taxed as ordinary income when shares vest is true for Cook and others who receive awards of restricted stock. However, in the more general case of employee stock option plans, taxes aren’t due until the option exercise date (or maybe not even until the underlying shares are actually sold), not at the vesting date.You pay normal tax like it was pay. This happens at the time the shares vest. The only difference is if the price goes up then when you sell them you may also have capital gains tax on the gain (based on difference between vest and sell price).
There can be other tax advantages depending on whether the options are qualified incentive stock options or non-qualified. ISOs are potentially taxed as long term capital gains and taxes aren’t due until the underlying share are sold, if certain conditions are met. (They are still subject to Alternative Minimum Tax however.) Non-quals are taxed as ordinary income at the time of exercise.