There would be no Windows license cost included in the price of the PCs because the OEMs would be installing OSX for you.
Unfortunately that is not the case. Whether or not an OEM PC has Windows installed, the OEM pays a fee to Microsoft for a Windows license and passes the cost of that license fee on to the customer.
It's a major - if not the major - reason Microsoft has been able to maintain such a stranglehold on the market with Windows. Whether you use Windows or not, you pay for it when you buy an OEM machine. So an OEM PC with OS X as an option would still have a "Windows Tax" attached to it.
Or in the case where you buy a Windows PC to put OSX on it, there have been cases where people had the Windows cost refunded to them.
Yes, with the expenditure of great time and money. Most people lack the will or the interest to do so which is why the "Windows Tax" is still levied and attempts to offer alternate OS' (like Linux) have been very unsuccessful for the OEMs.
And your last point is the point I am making. If OSX was to be made available to other companies then surely their offerings would be inferior to Apple's own and Apple have nothing to fear? But of course Apple have something to fear. They know their markups are huge and other companies could undercut them easily, so they continue to sell OSX on only their own hardware because they can keep charging a fortune for hardware.
And they use that money to continue to innovate, not just in OS X, but in other areas. How was the iPod's development paid for? Or the iPhone's? iTunes? iLife? iWork? If Apple's revenues go from billions per year to just tens of millions, they won't be able to afford to develop new products.
Microsoft is able to make Windows work because everyone has to buy it through those OEM contracts and therefore Microsoft needs to do nothing but collect billions of dollars every quarter from those OEMs.
Apple doesn't have that luxury and they're not going to be able to.
Apple may only have less than 10% of the PC market at the moment, but they have the most lucrative part of that market. So if Apple is charging $500 to $1000 more per PC than an OEM would, that means Apple has to sell 5 to 10 times as many OS X licenses (at $100 a pop) just to make the same amount of money.
I admire the optimism of those who believe that 25-50% of the world's PC buyers would choose OS X, but personally, I find the probabilities of that happening to be so low it borders on the farcical.
I cannot see how Apple could make more money licensing OS X than they do selling Macs. If it was a truly open market, it might be possible, but it isn't. Microsoft has an entrenched position that no government is willing to evict them from, preferring to just taking a ten-figure bribe (in the form of a "settlement") every couple of years to continue to look the other way.
Apple computers are expensive. I don't argue that. Even when Apple lowers the price, they're still expensive. But the public keeps buying them, even though they are so expensive. And I doubt it's just because of OS X. There are plenty of options (well, one less now) to run OS X on a non-Apple hardware and none of them require a PhD in Computer Science to do so. So for those who want OS X, but don't want to pay the premium of an Apple-branded computer, there are plenty of options available and many of them are literally "plug and play" (like EFi-X).
For everyone else, there's Macintosh.
