I've suspected the reason behind vendors not taking these steps has been the inherent difficulty of keeping interface and driver software current for the swiftly-changing specs of new devices.
When we've had devices in which OS specs did not change much over time (ie, Palm Pilot, iPod,) the proliferation of accessories and expansion products can be amazing. But in the rapidly-evolving smartphone arena, no one wants to try to keep up with that haphazardly-moving target.
OTOH, no vendor wants to lock down an OS for long, for fear of falling behind in the market (or being hacked and copied). So they keep making changes, even when stability could be in their best interest. It's a tough nut to crack.