Specs are required to run applications, which tend to have similar requirements in both Windows and OS X (with the exception of games, where Windows tends to be better). People need specs to run apps. Unless you can conclusively prove that OS X uses the the same specs as a similar PC running Windows, but uses them more efficiently in an application, then the OS is most definitely not a spec.
Just about, since it's been shown how much slower Vista runs than OSX and XP, and how much of an overall resource hog it is.
Go read the benchmarks available all over the net. But continue to argue on hardware alone, as if that really matters.