These comparisons are silly. Now imagine it's a BMW vs someone's project car both with the same $$$ invested. Yeah, the project car will probably smoke it. But not everyone wants a project car.
They should be doing this test against a Mac Pro if they want a fair comparison. And yes, the Mac Pro would likely be more expensive, but I don't think it's a surprise to anyone that building your own overclocked PC is cheaper.
A better example might be the cost delta between buying a car from the manufacturer and buying all the parts to make the same car separately and putting it together. The direct from manufacturer car will be far cheaper.