It's a fact of life that the vast majority of computer users buy their computers with the OS already installed, so as far as desktops and laptops are concerned it's a choice between Windows and OSX. But if you look at tablets and mobiles the proportions are very different. And for a large swathe of the remaining market for embedded devices it's Linux, period. I would bet that, in a large proprtion of homes in the developed world, there are more Linux based devices than all the other OSs put together.