Keep in mind that Apple could easily switch to AMD in the future.
Now that they're making the transition to x86, they have multiple CPU vendors to choose from. All of them are binary-compatible. They can use processors from Intel, AMD, Via, even STMicro.
They could even mix and match (e.g. Use a low-power Via chip in the Mac Mini, and use an AMD Opteron in the their high-end line).
Also, now that they've transitioned, they have more negotiating power. They can play Intel, AMD, and Via off of each other to negotiate for better pricing.
Basic rule in business: Commoditize your complements.
It's why the PC industry is so successful. It's why IBM endorses Linux. It's why Apple offers a not-very-profitable online music store.