Heh, I forgot about the contradicting opinions on pistol braces.
Taking a look at the receiver definition again I realized there are quite a few receivers that wouldn't be receivers according to the current definition. For example, MK I, II, III, 22/45, 700, any Anschutz, etc. The firing mechanisms aren't housed within the receiver.
I get the feeling the definition was written by someone who doesn't know a lot about firearms. This just seems like a bad idea in general, defining something one has little familiarity with... Makes one wonder why Laws are passed with such frequency by people with little to no expertise on the subject the Laws are pertaining to.