Market share as it relates to PC use is an absolute unmitigated canard and it's as misunderstood these days as it is useless for two obvious, basic reasons:
1) The internet. Designed from the beginning to be platform neutral, it doesn't matter which computer or OS you use, all that matters is having the ability to access the net. MS, initially worried that widespread use of the net could make it's Windows OS desktop dominance appear suddenly irrelevant, tried very hard to subvert the open internet principle and protect it's monopoly with it's "Windows Internet Explorer only" and "activeX" initiatives. But in doing so they also left the door wide open for Malware, Inc to rise directly in proportion. Slowly but surely, web designers now seem to be finally wising up, and generally it appears the net is in the process of correcting/curing itself with technologies like Ajax and a resurgence in adoption of standards-based products like Mozilla/Firefox and Mac OS X.
2) Every year, Apple sells computers by the millions, and that's really the most important thing. That means there are millions of active OS X users out there who don't seem to have a problem with supposedly paying a premium for a superior computing experience. That fact is bankable gold for software writers who are willing to produce quality software on the platform, because Mac users, millions and millions of them, by virtue of the fact that they demonstrate a willingness to pay for better stuff, will happily fork over their credit card for great third-party software. Another fact that developers seems to be slowly wising up to. You don't have to sell to every single Mac user, and it's unrealistic to believe you can. But how many units do you need to push out the door in order to make a handsome profit? 500,000? A million? That's a drop in the bucket in the Mac universe.
We have long since past the time when market share numbers, regardless of how they are calculated, are in any way relevant. The fact is in a world where general computer usage is as widespread as it has become nowadays with so many users of different platforms out there, market share for any given platform no longer matters. Once the number of active users reaches a certain threshold on a platform, they become relevant and that's what matters. Market share numbers, by their very primitive, generalized nature, don't disclose that fact, and arguably, have no intent to do so. It's basically an obsolete measurement from the pre-internet, corporate desktop days of the 80's and early nineties; much has changed in the computing world since then in terms of growth, users and technologies.
