Yes 100% jellybean is coming late this fall, Google pretty much said they have moved from 2 times a year to once a year release schedule.
Google's release policy is pretty straight forward. New beta version released in late fall, phones get updated by June with final version. And cycle repeats.
This is same cycle that goes on for ALL software. Take Mozilla FireFox for example.
https://wiki.mozilla.org/Releases
FireFox 12 will hit final on April 24th, in that time FireFox 13 will hit beta and FireFox 14 will hit Alpha(AURORA) and FireFox 15 will hit nightly. And this process keeps repeating. This is standard software release cycles.
The thing that seems to get to people is they are too used to not seeing this process behind the scenes and just get to see the final and that is it. But Android is open source so like most open source software the process is more transparent.
If you want to compare it to say iOS releases, look at it this way. June iOS6 will come out and your device will get ICS. Next June iOS7 will come out and your device will have Jellybean and etc. Whats eating people is they know it "exists" so they want it now and I don't blame them but if you look at it prospectively its the same release cycle, just more transparent.
There is no fragmentation, its a myth.