You seem to have quite an optimistic view on the benefits of software licensing. While I do think the consumer would benefit from a more open OS X licensing model, I'm not sure Apple would benefit:
1) If Apple enters an all software market, they lose a major selling point of their hardware and enter an area with more competition and a lower barrier to entry (see: Linux). OEM licensing could potentially be more profitable, but I'm unconvinced that the market for OS X is much bigger than the market for Macs - users, particularly businesses, are often held back by software requirements rather than by the price premium.
2) Apple likes dictating what hardware you purchase - cheaper, more standard tower blocks don't fit with its image as being refined and premium, and the netbook market has far lower margins than they currently reap on MacBooks. One MacBook purchaser could well bring more profit than 5-mac-netbook purchasers. Apple doesn't want to enter a race to the bottom - they make plenty of money through brands that are seen as higher quality.
3) Why? It gives them higher margins and it's unclear whether the market share increase would offset that.
Most importantly, in my opinion:
4) Apple is so profitable because they have created their own "premium computer" market that is far larger than anything held by Alienware or Dell's Adamo. They do this by creating products that appear relatively unique and are functionally different from competitors' equivalents thanks to unique software, design and minor features (such as battery life on their laptops). Without OS X, a Macbook is just another expensive laptop. There is also some level of positive feedback - unique hardware makes the software appear higher quality, which makes the hardware seem more unique etc - and some of the major selling points depend on hardware-software integration.
I'm not saying it isn't possible that Apple would benefit from opening up their software, but it's far from being certain.