As someone who works on Linux on ARM projects, I would have to disagree. There are good reasons to bring devices into the tree.
It really does make sense to have a single ARM kernel source with a device tree. This is not a single binary for all, but a single source tree. When you compile, it is not like you are getting all the bloat of a hundred different board packages. You use a different make script that pulls in the appropriate files. What it does give us is great templates to use when porting to similar sources.
If you ever take a look at board manufacturers' kernel source, each distribution is often very different from another. It takes a while to reconcile it with mainline kernel source. And it is even more of a pain to upgrade to a new kernel when a board maker had some whacky code placed in there. By at least placing it in the device tree, it gives them the incentive to use a template of code that already exists. Then hopefully some of us have an easier time porting when we want to upgrade Kernels and such.
I know it does not seem like it makes a lot of sense to some, but there really are good reasons for the change.
P.S. The unified Kernel is a Linux issue as a whole, not just an Ubuntu thing.