So starting with OSX, Apple has introduced 9 versions and Microsoft has introduced 4. Now, granted, you can't actually have upgraded from 10.0 to 10.9 because

So starting with OSX, Apple has introduced 9 versions and Microsoft has introduced 4. Now, granted, you can't actually have upgraded from 10.0 to 10.9 because of the dropped hardware support, but it would be interesting to compare the cost of upgrading through all the versions.