It's getting at the fact that PCs would probably need upgrading in order to experience everything Vista offers - which is true, is it not?
For example,
http://www.eweek.com/article2/0,1895,2068351,00.asp
94% don't meet the requirements needed for a experience of Vista Premium.
Exactly... EVERYTHING. EVERYTHING is not a requirement. Runs fine on my dev machine, which is over 3 years old and wasn't a top system then! Vista will run fine for even 5 year-old machines if you don't turn on all the gimmicks. I wonder what the latest OS X would run like on a 5 year-old Mac. I'm guessing the answer would begin with s and end in y. Don't forget MS like to make OSs as backward compatible as possible, something which would send chills down the spines of Apple developers.
Really? Doesn't run fine on a 3 year old (top spec machine at the time) at at work, doesn't even have any of the "trick" effects turned on.
OS X runs like s**t off a shovel on a 5 year old mac. One thing Apple have consistently done with every release is make it faster for older machines.
Dunno what you're going on about with backward compatiability? Apple have made 68K->PowerPC->Intel transitions and through fat (68K->PowerPC) & universal binaries (PowerPC->Intel) have made it seamless. Even OS X (PowerPC) is capable of running OS9 < applications through the classic environment.
Lets not forget carbon, which wraps the cocoa api (what native OS X apps are written in) in the OS9 (and lower) api up so that OS9 applications could run as native OS X applications with minor effort. Apple are still adding and expanding the carbon sdk with features of the latest versions of OS X.
No idea where you got this idea about!