That trend is something Apple learned from their marketing division having watched all the "suckas" constantly upgrading Windoze with those incessant service paks.
Kind of different, as the service packs are free, and as for incessant, there were 3 service packs for Windows XP over its 9 year lifespan.
I'd say that earlier versions of OSX on older platforms are infinitely more useable, stable and reliable than previous and comparable incarnations of Windows running on frankenPC's.
A copy of Windows XP from 2001 can be service-packed and patched right up to current, for free, while a copy of OSX from 2001 will have a hard time finding software to run, and will require you to spend money to upgrade it. Believe me, I've played with enough old versions of OSX to realize after a certain point the old versions just really aren't viable. Thankfully, it's also very easy to pirate, so I've never had to pay for a newer copy.