You don't have the right perspective. You look at things from an end user perspective. You are going to buy one processor, and you would like to buy Intel or AMD, and buy whatever is best today. Tomorrow the other brand might be better, and then you buy the other chip. Intel and AMD don't care.
That's different with Apple. Apple is right now Intel's number one priority customer. When Apple says "jump", Intel says "how high". On the other hand, when Intel wants to know what its customers want, Apple has some top developers who spend real time to give Intel answers that are really useful. For Apple to buy AMD chips would mean to throw all this away. They would be stuck with AMD for a very long time. If they wanted to go back to Intel, they would find themselves at the back of the queue. No more special designs for MacBook Air. No more faster clock rates than everyone else. No more Nehalem one month before Dell gets them.
A switch to AMD would only happen if Intel falls seriously behind and there is no way that they can catch up or come close for the next year. That is not the case at the moment. In most people's judgement, including mine and most likely Apple's, Intel is far ahead. AMD is trying to improve as fast as possible, but Intel actually has developments they haven't published yet, because they are so far ahead.