The "math" in this Computer World article is suspect, in my opinion.
I'd buy a Mac in a heartbeat if I had that sort of money. But I'd run Linux on it. If I left the Mac OS X on it, I'd have to purchase a LOT of software to meet all my needs. There just isn't a lot of freeware or free/open source software (FOSS) for the Mac and the proprietary stuff I would have to purchse is expensive. That's where the big difference lies for me. With the PC and Windows, I can use FOSS to fill out my software needs. With Linux, all my needs are met with FOSS. But with the Mac OS X, I would have to buy a lot of additional software.
Even with all that, this is an interesting comparison. Just don't trust other people's numbers too far.