General Aviation pilot questioned ATC's handling of Washington D.C. SFRA entry requests.

Narrative

While in smooth cruise autopilot on flight at 1;420 FT indicated; Controller asked twice what my altitude was and repeated altimeter setting. When I replied 1;440 FT he responded you are indicating 1;500 FT; and repeated the altimeter. I replied what my indicated altitude was and my baro meter was set correctly. I queried that maybe encoders reported in 100 FT increments. My concern is not an altitude deviation. My concern is that this kind of 'scary' inquiry and refusal for entry into Class B airspace is what likely killed the people in Phoenix. Controllers are for the most part professional and over worked. Naturally they want a lower workload and it has been my impression flying around the Washington DC SFRA that 'Remain clear of the Class B' is the first thing from their mouths. It is difficult to gain access to the B airspace; even if 2;000 or 2;500 FT is all you are requesting. Transitioning the Quantico very sparse area; especially at night; at low altitude is bordering on dangerous. Few jets operate at 2;000 [or] 2;500 FT [that] far from the airport. Why do they guard their space so intently? I understand that the Washington airspace is being redesigned. Please do not allow them to lower Class B; especially near the mountains in Loudin County.