For gamers, a low performance value yields a value of $10, and a high performance value yields a value of $12.
For professionals, a low performance value yields a value of $5, and a high performance value yields a value of $20.
If nVidia sold a single design to all of them, with a high performance value, then gamers would be willing to pay less than $12, and professionals would pay less than $20.
If they want to sell to the entire market, they have to price it less than $12, and lose around $8 from each professional buyer.
However, if they sell 2 designs (e.g: one a cripple of the other), they can derive around $10 of value from each gamer, and $20 from each professional.
The reason this is inefficient, is because for each gamer buying the crippled design, there is a loss of $2 of real value. This loss is a real value loss that could be avoided if there was some other way to extract the actual value for gamers and professionals without crippling the product.
In short, the inefficiency is not that the price is not near the production cost, but that the intentional crippling of the product (necessary to extract maximal value via market segmentation) is causing an actual value loss in the economy.