This assumes a shrinking pool. Open Source development is happening at a higher rate than ever before, and the number of Open Source developers and users is higher than ever before.

Yes, Apple has seen a dramatic increase in market share, but before that Windows laptops were abundant at Open Source conferences; before a few years ago, running Linux on a laptop was a harrowing and challenging experience, and most people (even developers) simply could not make it all work. I'm only on my second "fully functional under Linux" laptop, and I've always bought laptops with Linux compatibility in mind.

Apple happens to make the nicest laptop hardware, and Mac OS X happens to run best on it. And, for many tasks, particularly tasks common to laptop usage, Mac OS X is an acceptable substitute for Linux in ways that Windows never was.

Of course, I couldn't tell you how many of the participants are open source contributors.