When hardware and software are a cohesive unit it's hard to run something generic on the hardware, or run the software on some other hardware. That is not the case for Windows, Linux, and Android, which is why people feel differently about that ecosystem.
That must explain the lack of penetration of Android tablets! (They have no back button either)
AFAIK Android was basically unusable on iOS hardware, using the sleep/wake button in an odd way and other things that do not work well.
Nope. Only volume and on/off. At least that's what the Galaxy Tab has. As you pointed out, new versions of Android allow emulating whatever buttons the device doesn't have on screen. And the newest phones basically don't have any, relying entirely on the screen.
AFAIK Android was basically unusable on iOS hardware, using the sleep/wake button in an odd way and other things that do not work well.
This sounds like the port was botched. Nothing you said explains why it couldn't work. In fact the oppposite: you've already illustrated the button layout is irrelevant.