there are differences. For example, the profit from the grant date to the date of exercise is ordinary income - taxed at your bracket rate, while any profit coming from holding for longer than 1 year after exercise is at long-term capital gain - 15%.
the risk isn't the same. Instead of capital gain a capital loss may happen - for example when you own stock, like, in particular, after exercise. Whereis in case of stock options there is no risk of loss before exercise. The stock options may be worth 0 - that is the lowest possible outcome, and you wouldn't be charged a dime if the options are underwater. Just like bonus - company pays to you when things are great, yet you don't pay to company when the things aren't. Thus the same ordinary income tax treatment for stock options exercise profit as for bonus.
