Also don't forget that this $29 upgrade comes after happily paying $129 for every other upgrade for the past six years or so, as each upgrade generally came every 18-21 months.
So whereas one might have paid for XP and Vista over the course of five years, another might have paid $129*6 over the course of those same five years, meaning Mac OS X, coupled with the hardware, could actually be more expensive than Windows in certain situations.
And thus, this is correct. You must balance out the costs of the two. Windows licenses tend to be more expensive in the short term, but balance out in the long term because of the cheaper hardware and the fact that major Windows versions tend to last a minimum of 2-3 years, whereas it's very possible Apple will release 10.7 by late 2010.