AmiArcadia is a bad example.... at first AmigaOS 4 versions were included in the AmigaOS 3 archive. Then there was a long period of time when the AmigaOS 4 version wasn't updated but the MorphOS version was. There was also time when the opposite happened, as the AOS 3 version was the master version at first, and it was up to other people to port it to MOS and AOS - which happened at different frequencies.
I'm not saying that AOS4 has a much bigger userbase than MOS - I don't know if that's true or not - but I do know that you can't take one piece of software and if you had to do that, it should be a piece of software that was developed at the same pace on each OS.
Isn't this rather OT anyway?