Considering a vast majority of folks don't even consider upgrading their systems other than the enthusiasts of course, platform choice isn't really going to be major issue. General users buying prebuilt rigs are going to buy their i5, i7 or AMx based rig and run it until the wheels fall off so to speak without ever opening the case.

The difference I see with i7 & i5 vs s754 & s939 is that Intel released the high end platform from the start whereas AMD released the higher end platform later which left early adopter s754 users who might have wanted more performance with a limited upgrade path.