Microsoft is mostly a software company, they do not sell computer systems.
Apple makes money on both software and hardware and as such they have adopted a different business model.
And during your Mac's lifetime, how many times would change the OS before you're "required", or want to, exchange your Mac? Apple is expecting you to buy new hardware within a calculated timeframe.
So until OS X is a 'freely' available, as in not tied to one specific brand, there is little point in having a discussion in terms of pricing. And if Apple really had any balls they would start marketing OS X for other computer systems. In terms of either platform being largely cheaper, it's an illusion.
In terms of choice though - it's yours.