I will correct you because you are wrong.
Windows 7 had free upgrades if you bought a PC after June, Windows 8 actually has $15 (i.e. Windows 8 is costlier)
Windows 7 had $50 promotional price, Windows 8 has $40 (not much difference OR 20% cheaper in Apple style to make it look larger)
Windows 7 had $150 family promotion much after launch, Windows 8 has none like that.
Windows 7 had a "full" version for sale, Windows 8 doesn't have it.
Windows 7 had free upgrades, it doesn't seem people are rushing for a Windows 8 upgrade.
Windows 7 at $50 promotional price? Never saw that, really. I guess you'd have to really look for someone who got this price.
Windows 7 family pack was never available in Brazil, for instance... nor promotional prices. It actually used to cost over $ 120,00 (upgrade) and $240 equivalent and I really believe Brazil is not the only country with such a high prices.
Windows 7 was very pirated, because it was very expensive.
So... It may be selling 40 million, but those numbers are financially much, much lower than Windows 7 or even Vista numbers, as those $40 discount prices are actually everywhere in world right now, not only in the US.