C++ would certainly make the actual game code more portable than blitz as its not relying on a unique language
You don't actually code in C++ do you? Maybe C++ has changed in the last 5 or so years, but otherwise the idea that a game written in C++ is more portable than one written in any other language, is absurd. When porting a game, it is usually rewritten from scratch by a different (ie more experienced on that platform) developer. imho a game is not better when coded in c++.
The only reason most developers are still using C++ (as opposed to for example C#) is for legacy reasons. It's the language all of their other stuff is written in, and rewriting it would be a huge undertaking, and would require testing it from scratch.