Microsoft may have the numbers, but one thing Apple is really good about is getting people to shift their Macs over to the latest and greatest version of OS X in a timely manner.
For example, even though OS X Mountain Lion was only released in July, over 25% of all Macs ran it by October. OS X 10.5 Leopard hovers at a little less than 10%, while OS X Lion is on about 30% of all Macs.
What’s most surprising, though, is what operating system ties OS X Lion for the most popular version of OS X: OS X 10.6, Snow Leopard.