I'll grant you that because of the comparatively simpler semantics, you will find more platforms with C compilers available as opposed to C++ (although the comparison is a little off the point, since Dullstar has been using C# so far not C++). But that completely ignores the fact that not only the language itself needs to be multi-platform, but also any libraries you used for critical things like graphics, audio, etc, which aren't part of the language. Keeping that in mind, and you might find that other language's support for the most "common" target platforms are quite acceptable.
In any event, your program's multiplatform support is only as good as the number of platforms it has actually been tested on.