Most people prefer AMD. I think the main reason Apple went with Intel, is, like you said, marketing. Intel is huge, and is far more widely known than AMD. For the most part, AMD is really only known inside the computer community. Everytime I am asked to build a system for someone they always tell me they want "Pentium 4" because they know pentium. AMD has no commercials, and no advertisements. It is one of those companies that, for the most part, has been passed around by word of mouth. For a company to live like that, that is very impressive. I applaud AMD for this. But there could also be a method to Apple's madness. I'm sure they gave AMD a blow, and found that Intel works better. Apple is part of the computer community, and so they definetely know about AMD. But I think for the most part it had to do with politics more than anything else.
There is a reason Intel is so big, as there is a reason Microsoft is big. It's simple, it's because they are good at what they do. Is there any other reason they would be so big? No. If they werent good at what they do (Intel: Chips, MS: software) they wouldnt be so huge and Bill Gates certainly wouldnt be as rich as he is.