It's unclear why Mac users are holding on to Snow Leopard, but one factor may be that it is the newest Apple OS able to run applications written for the PowerPC processor, the Apple/IBM/Motorola-designed CPU used by Macs before Apple announced a switch to Intel in 2005. The first Intel Macs launched in January 2006.
(Snow Leopard will not run on PowerPC-equipped Macs -- the last edition to do so was 2007's OS X Leopard -- but it can run applications written for that chip via the Rosetta utility.)
Another possibility: Many Mac users dinged Lion for being less stable and reliable than Snow Leopard, and said they would stick with the older OS. Those sentiments have also been popular with many Windows XP users.
"I think [Snow Leopard] was the best OS they've made so far and I have no desire to turn my laptop into a smartphone by installing Mountain Lion," said one Computerworld reader in a comment appended to an Oct. 2 story, referring to several features that the latter shared with iOS, Apple's mobile operating system for the iPhone. "If I wanted a smartphone I'd already have one."
Net Applications measures operating system usage by tracking unique visitors to approximately 40,000 Web sites. More information about its October stats -- including gains by Microsoft's Windows 8 -- can be found on the company's website.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, or subscribe to Gregg's RSS feed . His e-mail address is email@example.com.