Are you seriously saying that you believe, in this day and age, that a $600 windows-based laptop won't last more than 2 years? I have a Dell laptop that I bought at the beginning of medical school, and I'm now in my last (4th) year, and still happily using it. I paid a little more than $600 ($658) for a Inspiron 6400 with a T2400 (1.86 ghz), Radeon x1400 (256 mb onboard, upto 756 mb shared, total 1 gb), 100gb 7200 rpm HD, 2 gb RAM.
However, the classmates of mine who bought a Mac at the same time (Fall 2005) got a system that won't run XP (since it's a motorolla RISC set-up), and have, as soon as they were able, either upgraded to an intel-based Mac or a windows-based PC. Office 2007 Ultimate set me back $60 with the Ultimate Steal deal from MS, while my Mac friends had to wait and pay full retail for Office 2008 (those who decided to upgrade).
And those who upgraded to the Macbook when it came out (a year after I got my laptop) got a computer with essentially the same specs as mine, with 2 differences, 1 good, 1 bad - 800 mHz FSB (mine was 600), and Intel GMA950 (built-in graphics card). Yes, after bootcamp finally came out, they could run XP, and thus some PC games, but the built-in graphics card limited the resolution and textures the computer would run.
I have never seen my friends with Macs get anything done more expendiently than me because of their OS. As you pointed out in an earlier post, MS Office runs on both OS's, and many other programs run through web browsers.