No phones run Honeycomb and I've run into very very few apps that don't work on ICS. Most phones are still on Gingerbread and it's been a little slow in moving to ICS but that looks to be changing very soon with many devices schedule for or are already receiving ICS.
Jellybean is only OS 4.1 (coming from ICS 4.0). Not really a huge jump, just enough to give it a new name....kind of like Froyo (2.2) became Gingerbread (2.3). Now we have ICS (4.0) becoming Jellybean (4.1).
The migration from 4.0 to 4.1 won't be near the jump 2.3 was to 4.0.