I'm sure they can sell more OS X licenses and increase their profits, if they release OS X for standard PCs.
But why would they make more money selling it for PCs?
The bulk of MS's profits come from selling an astronomical number of licenses to large PC makers (Dell, HP etc) and bulk licenses to big corporate computer users. How much they pay is not public knowledge, but common sense dictates that it's a lot less than the $100 (ballpark) for a one-off OEM license or retail upgrade. The "full retail" versions carry a bigger mark-up, but about the only people who buy those are Mac users since its the only legit way to get Windows for BootCamp or Parallels.
That's not a lot of money per PC - MS thrives because they get a relatively small income from more or less every PC sold.
Price-wise, Apple would have to compete with Windows - but they'd only sell a fraction of the number of licenses that MS shifts.
...but people would flock to buy cheap laptops and mini-towers running OSX, wouldn't they? Well, the problem is that they wouldn't be that cheap: Every time Dell or someone has offered a Linux-based PC it has come out at the same price, or even more expensive than their comparable Windows PCs - and Linux is
free (of course, there will be some costs involved but probably not a per-machine license fee). Why? Well, at a guess:
1. The really cheap PCs are made by throwing together cheap, commodity parts - because
everything works with Windows you can use whatever is going cheap this month. OSX or Linux don't have that universal support, so you start having to use specific, probably more expensive, parts.
2. Rumour has it that the big boys pay Windows licenses for every machine they sell and/or that MS hikes the license price if they sell non-windows machines. So, basically, you're still paying for Windows even if you have a different OS.
3. PC builders get paid for installing adware and demos on their system. Not very Apple.
Then, someone has to
sell these more-expensive-than-Windows OSX PCs to punters - and there's nothing more futile than trying to get a sales force trained to sell Brand X to start selling Brand Y instead.
You know how its going to go: Customer: "Can I do my home accounts on OS X?" SalesDrone: "Oh, you might be better off on Windows." Customer: "Can I read my Exchange email from work?" SalesDroid: "No, you'll need Windows". Customer: "What games are available?" Salesdroid: "There aren't many games for OS X". Why should SalesDroid worry what OS the punter chooses? They make ******* all money on selling entry-level PCs - the important thing is to sell them a credit agreement, extended warranty and a $50 HDMI cable -
that's what gets them the bonus.
No, sorry, these "cheap OEM Macs" ain't gonna happen - what you'll get is makers offering MacBookPro-alikes and iMac-alikes just undercutting the genuine articles by $100 or so to poach Apple customers but making no particular effort to open up new markets. That's what happened last time Apple tried licensing the OS.
No, Apple have found the best way to survive in a Windows dominated world: sell premium-priced laptops and small-form-factor systems with nice high margins, preferably from your own retail chains or "store-in-a-store" outlets with Mac-knowledgable staff - and use the cool-looking hardware to sell the software. Helpfully, most of the other manufacturers seem completely incapable of producing anything that doesn't look like a bucket of spare parts alongside a Mac, even if its technically better (its the "minimalism" thing - they just can't resist an extra bit of chrome, a bank of indicator lights, a plastering of stickers...)
