Hi Sgt,
Things haven't changed must since I wrote this:
http://www.guitartricks.com/forum/showthread.php?t=34594
A lot your questions are the same questions I have for video streaming (like Netflix, etc). Why can I get this movie, and not that movie? Why can't I get a TV show episode from 8 weeks ago, when I can get the episode from six weeks ago? Do they really expect me to go to a completely different service on a completely different device and pay $3 for a TV show episode?
Publishers I think would benefit from a centralized clearinghouse for licensing, but instead they make individual deals with everybody. We work with the system that exists and so far we have been pretty successful. There is a long way to go, as you note, but we are working on it.
When we do get permission, we make sure to teach the song right, and to film it right, and that is what I am most proud of.