As I said... C++ is a bad example, because borland c++, intelc++, etc. are all tools for c++, that fully support ISO-C++ and only extend the language. Take any ISO-C++ programm, it runs on every C++ compiler. Take any Delphi-Program it most likely won't work in mode ObjFPC as these two dialects are different in some fundamental language featues (e.g. function pointers, generics, operator overloading, etc.)
I mean sure the reasoning about wikipedia doesn't really make sense and this should be decided on a case by case basis (e.g. vb6 and vb.net are also distinguished and I think no one argues with that), but with this framework they are consistent.
The only exception I've found in their top 50's was LISP, where the original LISP language is now 70 years old and not used anymore, and all modern LISP dialects also have their own wikipedia pages.