You not getting it and it not making sense are two different things.
In other words, it makes no sense and you got nothing to backup your statements.
There are plenty of software only companies that keep quality high.
There are plenty of companies that develop for different hardware and they don't need to change the "framework" (still not sure what you mean there) for different hardware. Aside from technical differences, multiplatform games play the same. Hardware is irrelevant.
There is absolutely nothing inherent to the Nintendo hardware design that would prevent SMB3D World from running on a different piece of hardware.