The platform module is newer, I think (but still pretty old - it's in Python 2.6). There may be subtleties around cygwin, but I don't use that so I'm not sure. Otherwise it's probably just what people are used to.

BTW, what versions of Python does invoke support? (Python 3.3 has os.get_terminal_size, not that that's much use for a few years yet :-))