I think the difference is, most people recognize that there is a place where C is really your only choice. Maybe you need a little shim code to interact with a shared object in another language from ML or something. It's harder to argue that for C++ or Java.
Other than when compilers are simply not available, a rare occurrence these days (and I will argue "missing the point" if that's the only important property of the language), I am having a difficult time imagining a situation where C works but C++ would not.
