This is true, mostly because only one company in this space lumps all their phones under one name even when they are on different carriers with different radios and firmwares... until the GSIII that is.
I could be wrong, but I remember reading that there is only 1 hardware model for the iPhone 4s. It supports both GSM and CDMA networks. The wikipedia article seems to support this claim: http://en.wikipedia.org/wiki/IPhone_4S#Hardware
That is correct - all 4s devices have both CDMA and GSM support; the difference between the AT&T and Verizon "versions" is just one of activation, basically.