I think they would have been just as successful. Most people don't care about the type of chip in it (to most people, a processor is "the pentium bit"). To most people, perceived performance is more important than actual performance. A slow chip that seems fast will be chosen by the average consumer over the the faster chip that seems slow. This is the beauty of Mac OS X - it gets faster on the same hardware (assuming the hardware isn't the minimum supported, etc).
Most people buy the Mac for iLife, iWork (although to a lesser extent), etc; not for the chips. When spouting about how good my Mac is, I always mention the ability to run Windows as a 'just-in-case' feature - a feature that sounds good, but when it comes to actually using it, no-one actually does. I realize that some people will use it, but I would say about 90% dont.
And lets face it, looking at history, Apple will switch again in 2015 or 2016 (although in reality, if Intel keep up their speed advantage, I can see Apple staying with them indefinatley. As long as they don't do another NetBurst
)