Apple already tried that. It darn near killed the company.
By the way, current projections say that Apple *will* have 40% of the new computer market... by 2010.
Apple is a different kind of company now. Their iPod brand is the major driving force of profit. They have AppleTV, the iPhone, accessories, and their own application software. They sell music, movies, television shows, and ringtones.
Licensing companies to sell their own hardware with OS X wouldn’t be the same as it was for Apple pre-iPod.