I'd say that Google is responding to pressure from customers who want to buy "stock" Android. Also, Microsoft took noticeable pleasure in restricting its Windows Phone 7 vendors, as it also increasingly restricts Windows licensees (relative to the earlier days).

Frankly, I'd be perfectly happy for Motorola to use their stable of developers to debug the device drivers. I'm annoyed that WiFi doesn't work anywhere near as well on my Android as it did on my earlier iPhone. Bluetooth also seems more prone to drop the connection, particularly with my car. I'm sure some of that blame rests on Google (or on Linux), but that's where Motorola could really contribute. They know how to do real-world testing and could generate really high quality bug reports.

Likewise, if the hardware vendors focused their efforts on good hardware support, then presumably it would be much easier for them to port their changes forward to newer versions of Android, bringing newer versions to their customers sooner.

Oh well. I can always upgrade my Droid X to an apparently leaked build of Gingerbread (apparently an official build from Motorola that Verizon rejected, perhaps because it mentioned AT&T inside the tethering app... oops), using techniques that will brick my phone if I screw something up. Or I can wait. And wait.