Man... I don't know if this will change anything. I was out just recently walking with a RCExplorer tricopter to the ball parks near my home where I do all my maidens and test flights. Never when there's a lot of people around. This time, it was just me and a park ranger who was loading his trailer with his horse. When I passed him, I greeted him with a smile and a hello. He said hello, but then added "You know, you're not supposed to fly that here." This confused me because I know I've flown these things in open view with other park rangers watching and have talked to them about my RC flying. He added that it's because we're within 5 miles of Logan airport. He added, very nicely, if I walked to the park in the next town over (I'm in Boston, on the border with a town called Brookline where there's a nice large park pretty close, but still a good 15-20 minute walk away), I can fly because it's outside the ring.
Now, I've checked... Heck, even my apps (EZGUI) that warns about proximity to airports tell me that it's ok to fly at this park. I didn't want to argue and figured he wouldn't say that unless his superiors briefed them on it. The fact that he just wanted me to fly at a park that was nearby but further from the airport (by something like .5 to .75 miles) told me it's some some silly regulation people have decided to impose for the purpose of CYA.
Anyway, as PsyBorg fears, I think that even if the FAA can't impose registration requirements, it's really kind of open season for local municipalities to make rules that are roughly based on the FAA rules. I could have gone on about how, I just needed to call the Logan tower to fly my tricopter for the 10 minutes I planned in order to get a tail tune completed. Instead, I walked the 15 minutes (30 round trip) for my 10 minute flight.
BTW, I just used Google Maps to measure the distance from the tower to my closest park... 6.1 miles. Meh... What it could be, and this may be a distinction even he wasn't aware, is that this is a regulation imposed not because of Logan (even though he mentioned it) but because of all the hospitals near me, especially those with helipads on their rooftops. We do get a fair amount of helicopter flights in this area. The state police also seem to use the park area nearby for either helicopter patrols or training because their EC135/145s are quite distinctive and a constant presence.