I think it's more to do with the fact that the programs are absolutely terrible on Windows, not how they look. Plenty of different looking things on Windows, and the users generally deal.elppa's suggestion is really the right one. If you intend to write applications on MacOS X that are even close to feeling like MacOS X applications then you need to code the GUI's with the AppKit (Cocoa) Framework. Anything else is going to feel alien, and MacOS X users are sensitive to that.
You can still build all of of your logic in C++, but you need to have clean separation of your program logic and the presentation system. If you are doing it right you already have this, and this division should be easy.
My interpretation of Supershane457's objections boil down to his/her being used to one way of doing things (some C++ library) and reacting negatively to a new way doing things (AppKit/Cocoa). If you are going to work on MacOS X, then you are going to have to get used to the way of doing things here. Swimming up-stream is not going to be very productive.
 They are not the only ones, look at the gnashing of teeth on Windows over iTunes and QuickTime which feel non-native there.
I tried their OpenGL Hello world program, and guess what happened? The OpenGL subwindow, which was supposed to be confined with the area of its widget, instead appeared outside of the main window. I ran the code a few times and it appeared a different spot on the display every time. I've got no time to wait for Nokia to fix such basic bugs.Of course there are people paid to work on (Qt). And it works well.