Writing C++ for Unix/Linux is same as writing for DOS.
That is not true. Basically, developing command line tools is very similar in any Microsoft OS or any other OS, that you can get a compiler for. So what you mean is: "Developing command line programs for Linux is the same as writing them for DOS." But in Linux you can use powerful graphical libraries too! (GTK and QT being the most widespread ones.)
Personally, I develop all my programs in Linux, but most command line tools should work on any system you compile them for.
Greetings,
Nepomuk
PS.: I'm guessing, that you're only really interested in Windows OSes, as you've asked this in the Windows Forum. If you want to know the differences between developing for various Windows versions, the C / C++ Forum may be a better place to ask.