So Apple has to keep making Macs, but they don't have to improve OS X. (When's 10.7 coming out?) Not an auspicious sign.
Next year, maybe? They just released 10.6 last year. Do they need to do a release every year?
10.7 isn't being shown at WWDC, so it probably won't be released in 2011. Since 10.6 had very few visible new features, that's a long time to wait.
What new features would you want? I still use Tiger on my primary machine and haven't missed much (outside of performance boosts) in the subsequent releases.
There was a time when Apple's ability to ship a new OS every 1.5 years was touted as one if proudest accomplishments. MS was insulted for years over their inability to ship a new version of Windows.
Desktop computers (and laptops) aren't advancing at the same rate that they used to. Also, OS X has matured tremendously since its reboot of the Mac OS. Maybe there's just not that much left on the queue.