Quoting the About The Setup page:

"Despite appearances, the site is not actually sponsored by Apple - people just seem to like using their tools. We're a fan, too."

However, I wouldn't be surprised if there was some selection bias involved. On the other hand, they sometimes feature such hardcore geeks like Russ Cox running Plan9 from User Space[1].

[1] http://russ.cox.usesthis.com/

You'd think that, because I myself use a Mac, but I'm more interested in the people over the hardware and pick based on that. :)