The way I always thought Apple avoided Anti-trust is that it controls the entire stack from software to hardware. The fact that they let you develop any apps at all, for any of their platforms, is their choice which they should be able to deny at will. You as the consumer don't have to buy their things if you don't like their policies.

Contrast this with Windows on any number of manufacturers of PCs. Where Microsoft went wrong is that they said, "We'll give you OEM pricing if you agree to this, this, this and this. Otherwise we'll make it difficult for you to compete." It's that sort of bullying that's a problem, because they don't own the entire stack.