I think you're confusing special and general relativity here. The equivalence principle in accelerated systems only holds true for infinitesimal regions of spacetime.
In the sense that an infinitesimal region of spacetime is a "perfect" reference frame, sure. But for the scales we're talking about, the equivalence principle gives a very strong approximation of the situation. Remember, we are extremely small!
(Some people don't even believe the Earth is round. They think that their local tangent space is all there is too it! That's how small we are.)
The equivalence principle is the opening from special to general relativity, I don't think ajconway was confusing the two at all!
