That's not surprising. Even if the housing wasn't so similar, there are not that many mic companies who make their own capsules. That's true for any type of microphones. Two companies I know of that make high-end measurement capsules are Brüel & Kjaer and Microtech Gefell, and those are orders of magnitude more expensive than the mics we're discussing.
I have read reports recently about another manufacturer of expensive and well-regarded measurement mics who does not manufacture their own capsules, but purchases them wholesale like the cheap mic companies do. I'm not going to say who it is until I can verify those claims, because it would be a bit scandalous given their prices.
@voltronic - do you know of any other reasonably priced mics apart from Dayton EMM-1 and Behringer EMC8000? Any Chinese solutions that are reasonably priced and do the job well?