umrigar, you're missing 10.4 Intel, released January 2006.
Even El Steveo considers it a full OS release.
http://www.macworld.com/articl.../2007/05/steveatd.html
"We?re also always improving our OS, generally have a release 18 months or so. And we had a big release we didn?t get much credit for, which is Mac OS X Tiger for Intel,?
You're also pretty misleading with your Windows release dates. You're listing server/workstation-class with desktop consumer OS's. In the PC world, there is a difference. Different teams with different timelines completely independent of each other. So for the Desktop it would look more like:
June 1998 - Windows 98
May 1999 - Windows 98SE
Feb 2000 - Windows ME
October 2001 - Windows XP
January 2007 - Windows Vista
Server would look like this:
Feb 2000 - Windows 2000
March 2003 - Server 2003
You're simply padding your numbers here with the x64 versions.
I don't count Windows 98 and 98SE or 10.0 and 10.1 as separate releases. These are merely incremental improvements on each other. 10.1 was also given to all 10.0 buyers for free.
Now I'm not here to say one approach is better/worse than another. You could look at it both ways. You could say that it shows Apple has a poor OS because of the need to release a new version every year. Or you could say that Apple has a commitment to perfection. Honestly, I don't care. I use both. I use OS X as my primary machine now that it's back from repair.
The fact remains that Apple has released a consumer desktop OS every year since 2001. Granted, since OS X's inception it had been compiled for Intel processors but the OS itself and applications therein were never fully debugged or prepared for retail release.