When you make 15 Billion, you probably don't care too much about the price of the house you bought last year was. Especially since you most likely don't have a mortgage.
I would question his financial acumen if he doesn't have a mortgage. Houses (specially the expensive ones) are a bad place to have money parked. Although, it doesn't make any difference in his fortune, anyway.
You're still viewing the house as an investment and not a purchase.
You're not parking money, you're buying a house, the same way you don't worry about the resale value of your TV, you won't worry about the resale value of your home. If you manage to sell the TV at a gain, wonderful, if not, no worries.
