This my friend is a long running question that has been going on for years now.
And the most simple answer now is brand. The average consumer does not care as much for specs and the true capability of their machine as compared to having a recognizable brand that will make them look cool as well as a very user friendly interface (not that I'm saying Windows is a hard interface to use, I would like to see the average Joe use Linux). Furthermore they just like to have the assurance that their product is stable so that if anything ever goes wrong someone is there to fix it for them. Finally the looks, although I will say Apple Macs or any branded PCs for that matter don't even hold a candle to how sexy you can make a custom built PC look.
Well you know the old saying "Don't judge a book by its cover" right? Well yea thats exactly what people are doing, they are judging Apple products by how they look and how easy the interface is to use, not what their true capabilities are.
