I can build my own PCs, and I have built maybe 20 of them for friends and family over the years. Handbuilt PCs are among the cheapest you can get, especially if you just keep upgrading (my dad's went from a 486 all the way to Pentium 2 before the casing had to be replaced for the Pentium III). But I'm still going to go buy 2 Mac Minis for my apartment.
Money is not always the issue, especially in a society caught in the throes of a consumerist-materialist world. So please do try not to be so shallow with the cheap PC arguments: it's not all about sheer economics.
There's a reason why some people buy a Honda when they can easily afford a Kia. And a reason why some fork out for a Beemer when a Honda would do. After all, they are all cars, which do the same basic thing. So you have to ask why.
The answer is obvious: lust. I'll be buying the Mac Mini even though I am perfectly capable of building my own shoebox-sized PC because I covet it. Pure and simple.