You, as a wage earner have to pay your taxes every year on your income for that year. So if you have a one-time windfall that makes you a lot money you could end up in the top tax bracket. But if you're a corporation you are allowed to reach forward with deferrals for years. Over a 45 to 50 year period, you can balance out the winning years and the losing years in such a way that you pay very little tax, especially considering the time-value of the money.