I understand your frustration with the pricing for Vista, et al. But honestly, all the various iterations of Mac OS X are basically small tweaks and small feature addition to the original. And for that, Apple charges for almost each and every minor upgrade, justifying their changes by calling it something -- Leopard, Panther, Tiger etc. -- and charging the consumer. Additionally, many times software patches are need to make your existing programs work with these OS X tweaks.
Microsoft -- good or bad, doesn't matter -- does one major OS revision every few years (in this case, over five!), and doesn't charge you for the patches and corrections.
This isn't a battle of the OS, it's the difference in the business model. My wife works on a Mac (graphic designer). She's laid out over $500 in recent years for her OS upgrades. In that time, I've laid out $0 for my WinXP Pro. The way I see it, I'm further ahead. And with what I spend every year in software upgrades, Windows is the least expensive on my list.