Pros may be a silent minority but it'd be outrageously stupid for Apple to underestimate their actual worth for its ecosystem and marketing.
Pros make software for iOS and OS X. You can make yet another twitter client on your Mac Mini, but it won't do if you're developing a huge 3D action game for future hardware.
Pros push the technology, which can be later adapted for regular users. There wouldn't be iMovie without Final Cut. There wouldn't be so many Final Cut users if the best hardware Apple could offer, was iMac.
In the end of the day pros are extremely influential opinion-makers. Being a satisfied and experienced Mac user and a "geek friend" of my friends, intentionally or not I introduced at the very least five new users to the Mac platform, and helped them learn it and tackle the difficulties. I'm sure this is not an uncommon situation, but you won't find statistics anywhere on how it impacts the sales.
Instead people count the amount of pro users and multiply it by the price of hardware they often use. Think wider!