Currently there is not a way to break down operating systems by version for Macintosh. For example, OSX 10.7 will display as the same operating system as OSX 10.8 in SiteCatalyst's operating system report - both reporting as Macintosh. This same report will break down OS for Windows by version, XP, Vista, 7, etc.
Our tech and quality assurance teams can only support a limited number of operating systems when building and testing a project, and knowing the breakout of Mac OS would allow them to choose the version that is most popular among our site’s users.