Don't forget AIX is a commercial product, like Windows, and according to the size of the server, so is the price of the OS, counting to (sometimes tens) thousands of dollars, for each systems. The prices are not fixed, discounts may be done by IBM, and the more important, as there is a price for the OS, some discount may not go the customer, but to other hands.... Think about it...
Don't forget AIX is a commercial product, like Windows, and according to the size of the server, so is the price of the OS, counting to (sometimes tens) thousands of dollars, for each systems. The prices are not fixed, discounts may be done by IBM, and the more important, as there is a price for the OS, some discount may not go the customer, but to other hands.... Think about it...