There is one single, very easily explained reason for this:
A COD-fan comes in to a computer store and says to the clerk "I want the new COD:Ghosts, going to play it on my PC.
The clerk answers: "Have you made sure your PC lives up to the minimum specifications?"
Then one of two things can happen.
1.
Either the COD-fan doesn't have that much money, so he looks at the minimum specs. "Oh I need to get some RAM... Luckily thats cheap. Oh and whats a 550Ti?"
Then the clerk says "It's cheap, but you should go for the 660. Or why not the 760?"
Maybe the COD-fan buys a 550, maybe a even a 660 or 760.
Nvidia highfives Activision "yaaaay!"
2.
The COD-fan has a lot of money, so he says "MINIMUM specs?! I want to run it at recommended, at LEAST". He looks at the recommended specs. "Oh I need to get me one of those 780 GTX cards. I only have an old 680!"
Nvidia highfives Activision "yaaaay!"
The real story is that both these people actually had computers strong enough to run on minimum and recommended, respectively. But whats the fun in that, says Nvidia and highfives Activision.