Usability is king

I tend to disagree, since the form factor determines the applicability of user interfaces.
The poor adoption of Windows Mobile, and Symbian (prior to Symbian^3) can be - at least partially - attributed to inadequate user interfaces.

Insisting on having the same UIs on desktops (with pixel-accurate mouse) and touch-enabled devices with cramped screens almost seems like a recipe for another half-baked product.

So no, it does not seem so obvious nor inevitable.