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.
WTF?
I code in C/C++ as a Game Programmer at A2M. We develop games for PC, PS2, Wii, XBOX360 and PS3 (as well as DS and PSP). The game I have been working on for the past year or so (under DNA, not announced yet, will be around October) will be released for both Wii and PS2 with the possibility of a PC version. And I can tell you, the code is almost exactly the same for all 3 platforms. The only things that change is the underlying engine (we have an engine for all platform with the exact same APIs) and the obviously different control schemes and the TRCs. The AI is the same, the jumping code is the same, the menu code is the same.
Same thing when I worked on Scooby-Doo Unmasked, we released it for PS2, GameCube and XBOX. It was just a matter of recompiling and burning a new disc.
Just look at Ogre, you've got the same APIs for Windows, Linux, Mac, and using either D3D or OpenGL for Windows. Your game code just needs to be recompiled on the proper platform and will remain mostly the same except for a few #ifdefs here and there.
Game logic doesn't change from a platform to another. Why would you even need to re-write from scratch? API calls to move a 3D object, animate one or draw GUI should be the same, except handled differently by the engine depending on the platform.
Now, do that with Blitz3D.
Also, before you argue that you said "usually" and that my place is different than most, I know people that work at Ubisoft and others that work at EA, and it is done the same way as us. Doing otherwise would be completely absurd and a giant money loss.