The way I understand it, is that the dyno gives you a controlled environment in which to test the settings of the fuel management unit under heavy acceleration, therefore making sure the settings are correct. The dyno settings get "mapped" to the PCV, which insures the bike always (in the optimum environment) performs the same way it did while on the dyno. The Cobra PowrPro Auto Tuner doesn't require a dyno, because it dynamically adjusts the settings for the current environment. But, units like the EJK / G-Man Bully offer more flexibility, because you can tune it in real-time, even while you're riding the bike. The PCV, again from what I understand, has to have a pre-programmed "map" uploaded to it, so it knows how to control the injectors. If you ride in a drastically changing environment, the PCV will be less effective, because it has a map for a different environment. (Humidity, elevation, etc.) The Cobra Auto-Tuner would, in theory, adjust itself to what it THINKS is the best settings for that environment, and the EJK/ Bully you could adjust manually for the best results.
I could be WAY off, but from all the research I've done, that's the way I understand it. ;-)