I got a call back from the Bureau of Marine Patrol in response to my email. The spokesperson (What do you call him?) emphatically pointed out that NH law overrides FAA regulations and didn't know how anyone had got the idea it didn't. (I had described a little of the discussion and questions people had raised on this thread).
He referenced RSA 270:12 (see
http://www.gencourt.state.nh.us/rsa/...270/270-12.htm) especially the 2nd paragraph. He said he didn't have in front of him when the restriction on Pickerel Pond was passed (I got a call from the state on a Saturday!!!!) but that I could call Monday to have someone look up when the restriction on Pickerel Pond was approved.
So, pending clarification of when the regulation went into effect, I would suggest this does settle the question of whether seaplanes are prohibited on Pickerel Pond.