Doesn't really seem like something the feds have any jurisdiction over, but ok...
I remember way back when the Droid Bionic was still getting updates, one of the users here was instrumental in helping with root and leaked updates to try. He claimed to have a Verizon contact and went over how version supposedly tests phone updates.
Verizon would get the update and run it through their battery of tests. As soon as it failed one test, the entire thing was scrubbed and went back to the developer to fix the problem. Then they'd get the updated version and start the test again from square one until it failed another test. They would do this over and over again until the update passed every test. Why they don't run every test, then send it back to the developer to try fixing everything at once, who knows. But their testing process seemed to be the biggest delay in rolling the updates.