The analogy is flawed. Consumers don't get locked into a 2-year contract forcing them to shop at Walmart exclusively. If they did, and Walmart required, say, a cut of all DVDs purchased for play on a Walmart-sold TV, I think that certainly would qualify for restraint of trade. Target could push their DVD prices all the way to zero and shoppers would still be stuck with their Walmart contracts.

(edit for those not reading carefully: Saying that the contract is willful has nothing to do with the argument. Consumers do not sign contracts with retailers. So applying logic about retail sales is a flawed analysis. Doing things like leveraging the illiquidity of platform choice to increase prices in a way that would be legal for a retailer is not, necessarily, legal for a platform vendor. Apple has control over the market that Walmart does not. That's what the whole idea of "restraint of trade" is about.)