I think it's less to do with C++ people first seeing C as much as it is about people getting into OOP and first getting used to structured programming. I've seen plenty of coders who've not seen C prior to C++, but knew Pascal really well, and had little trouble learning C++. And if you're talking about a teaching tool for training people to do structured programming, Pascal is a wonderful language.
It's just that learning things like OOP and templates and such is easy enough, but learning the finer points and minor annoyances that come with, say, extern functions in an ASM file or linking in ill-documented 3rd-party libraries and such are all the sort of thing that can only come with experience. I wouldn't expect the hobbyist programmer or the CS student to have seen these sorts of things as often because the projects are too lone-wolf style.