Didn't mean to imply you specifically regarding the evidence. I merely wish there was some evidence to back this "notion" about PC's vs. Mac's with regard to stability (post-Win2k of course ).
It's a many fold issue. I've been working on Apple's since the IIE came out, and there was a time that the 2 platforms could not have been any more different. Even still, Apples would have their share of issues as did PC's.
As the PC became more popular, more pieces of software became available for the platform, and as the market expanded you had more 3rd party developers enter the market, which let to tons of buggy software. Apple was a lot better certifying software for their machines, in essence because they had to be (if you are gonna have less software it had better be good) and therefore the platform over time appeared to be more stable (I'm generilizing a lot here as I'm squeezing 25 years into a paragraph).
At this point the OS's offer different flavors as well as functionalities, but in essense they are both sufficient in terms of operability and reliability.