I think to keep coming back to this is a losing argument. The clone experiment was a disaster for numerous reasons that had little to do with the concept of licensing an OS. Apple was getting annihilated in marketshare, the company was a rudderless ship, they were literally headed towards bankruptcy or being bought.
The reasoning is more likely along the lines of: Apple doesn't need to. They have a gazillion dollars, they have a very strong market and product brand that they don't want to mess with, it takes resources they don't want to spare, and there's only a small fraction of the market that can't find a usable Mac from the current product line (whether it's a perfect fit or not). If there's literally something you can't accomplish on a Mac, it's either because they don't make an OS X version of the software, or you're a 2% niche. And Apple doesn't serve 2% niches. There's a very vocal crowd around here who will never get it, but the market for HP tower workstations is getting smaller, and the market for OS X on HP tower workstation hardware is miniscule.
Personally, I see it as a mistake for Apple to abandon the tower workstation market just as I see it as a mistake that they don't offer some sort of xMac. But that's my opinion and I have enough smarts to understand that Apple's vision doesn't include those offerings.