This is not a long analytical piece but just an observation I felt I had to write down. Please keep this in mind when you want to comment on these thoughts.
OS X updates may be much cheaper than Windows updates, but OS X versions have a much shorter lifespan than Windows versions. Add to that the costs for updates of other software you use on your Mac and suddenly you are paying way more than Windows users.
Take Windows XP for example. This version of Windows was launched in 2001. More than eleven years later it’s still used by many people and a lot of new software you can still run on XP. As a contrast, take OS X 10.5 Leopard. Launched in 2007. A lot of new apps and software don’t run on 10.5. The minimum OS X these days is often 10.6 Snow Leopard, but sometimes apps already need at least 10.7 Lion to be able to install them.