>>> Why don't os4 programs not run on morphos and vice versa?
>>> All powerpc and all like Amiga, can't be that hard.

>> At least we have OS4Emu.

> what IF we started with MOS 2.x as AmigaOS 4 […]?

MorphOS 2.0 was released in 2008 and thus years after OS4.

> Its a bit like asking why MacOS X PPC, WinNT PPC and
> Linux PPC apps dont work in MorphOS since its all PPC,
> or Linux x64, Windows x64 and AROS x64.

The key phrase is "all like Amiga" here, I guess. Both being AmigaOS 3.x descendants, API relationship between MorphOS and OS4 should be way bigger than between Amiga-like OS (MorphOS/AROS/OS4), POSIX OS (MacOSX/Linux/…) and Windows.