Comparing to my no-longer-supported device, even when the apps that exist continue to work, sometimes the technology they have to communicate with in the outside world changes, rendering them practically useless. An example of this is the twitter client for my Nokia 810. Even though the app itself continues to run on its now unsupported OS, twitter changed its API in the mean time. Since very few developers are still maintaining apps for this device, let alone writing new ones, there's no one to incorporate these changes into the app to make it actually work.

Granted, since a lot of people have Android phones, and there must be a bunch still in the 1.x stage of life, it will probably take a while for us to get to the point where we start listing apps that DO work on 1.6 vs those that don't, but that's another long-term worry if the edge doesn't update Android versions.