I recently read this: http://news.ycombinator.com/item?id=3362072 a post by user "calloc" which I find quite interesting. I personally work for Absio Corp (http://absio.com/) and we do Android development for the DoD and we too have found many of the issues that I've mentioned above and that calloc has found as well. At the moment we are testing on the Evo 4G, Photon 4G, Samsung Galaxy S II, and the Droid X, with a couple of other devices mixed in. I believe we also got a new Galaxy Nexus that we are testing on.
It's a pain, and we've had issues with bugs only cropping up on one device but not another (even if they have the same Android version).
The current strategy for android is to keep pushing the device level up through app developers rather than through carriers. I'm now at a point where I do all my devs targetting Ice Cream Sandwich and including the compatibility packages for older versions. This does not fix all of the fragmentation you're referring to yet, but it's a very definitive step forward. Of course, this essentially means that potentially all my apps are carrying the same patch of the OS with them...
Anyway about 80% of my previous fragmentation issues were solved with ICS. The remaining 20% though, are the truly hard ones!
It's a pain, and we've had issues with bugs only cropping up on one device but not another (even if they have the same Android version).