The bottomline is that Apple is evolving at an ever increasing pace while Windows is stagnant.
From XP to Vista there was a devolution instead of an evolution and from Vista from Windows 7 they recovered some ground but it is still not that much more attractive than XP from a purely technical and experiential point. So basically the technology has been stagnant for about 8 years. 8 Years!!!
Cocoa is now 64 bit and with Open CL and GCD technology writing applications that take full advantage of CPU and GPU is a breeze now. Expect developers to start writing applications for macs that takes a third of the effort compared to the same application for Windows but delivers 3-15 times more performance.
That disparity is only going to increase in time since i) low level coding technologies are going to get honed while, ii) Windows will continue to be stagnant because an OS built on a rotting foundation of legacy DLLs and other junk simply cannot improve anymore. Microsoft also cannot chuck their OS and start anew as that would be handing over the market to Apple even faster.
For those that say that 50% marketshare is not attainable because of price, I remind you that an enterprise level Windows PC is the same price or more expensive than Macs. If you buy a fairly standard $1000 PC desktop system, in 12 months it will be worth zero dollars as you won't be able to sell it at all. If you buy an iMac for, say, $1500, 12 months from now it will be worth about $1000 on the used market. In the meanwhile you are using a much much faster computer that is slicker, silent, has better display, etc, etc.
In summary: Microsoft is a branch in the evolutionary tree that did well for a while but then became irrelevant and extinct.