[Retric]

It's the same basic concept as product placement in movies. The whole point of the program is advertizing. So, if you place the product in a negative light then the whole idea is wasted. (AKA, coke is not going to pay for a spot where someone says this soda is terrible bring me a Pepsi, even if the coke get's airtime and people see the bottle etc.)

PS: I don't know the details but the discount could easily drop the price well below apples production costs. And apparently you also get the right to use some of their IP (advertizing copy etc?).