I saw an article a while back, just before 7 released, talking about PC cost vs. Mac Costs, and apparently mac, just the OS, comes out to costing more over time because of the constant stream of upgraded versions compared to windows. Because windows versions are fewer and far between, but cost quite a bit more.
I'm calling BS on that one. Nobody has to upgrade their Mac OS if they don't want to. It's highly worthwhile to keep current, but the same could be said of Windows.
As for Windows being faster than MacOS for some things: umm, yeah. The architectures of even the most fundamental things—like the IO subsystem, VM subsystem, networking stack, and especially the kernel—are completely different between the two. In my experience, Apple prioritizes user interface responsiveness above all else, and that has its cost in terms of raw performance. It's also one of the many things that keeps me using Macs despite the greater hardware cost.
It's also not surprising that Windows 7 is actually slower than XP in most cases. XP came out in 2001, when computers were a lot less capable. It does less, and does more with less hardware. More than that, Windows 7 (actually Vista, but most seem to want to pretend it never existed) modernizes many systems, most notably the graphics stack. A modern compositing graphics stack takes a heavy toll, but it's very much worth the cost.