Macs retain their value for longer. People still use their Macs for years after they've been discontinued. I personally plan to keep my MacBook for 7 years without another format (I did one to get more HD space). I plan to do 1 or 2 more upgrades (a 200GB HD from Toshiba in about June) and an external monitor when I get a desk in my room. After that, maybe an external DVD Writer and I'm set for the next few years. I will do that because I know Mac OS X doesn't get as clogged up on older hardware as Windows does. I can practically guarantee that my MacBook will be able to run at least the next 3 versions of OS X, because of historical records. A Mac bought at a time when OS 9 was commonly used will still be able to run OS X 10.4, which is more than 3 versions of the OS.
In contrast, my HP desktop which is probably 3 years old now (roughly) cannot run Windows Vista at a satisfying speed.
In contrast, my HP desktop which is probably 3 years old now (roughly) cannot run Windows Vista at a satisfying speed.