the Cybus Cyberman were really just a modern update on the older design. Since the Mondus Cybermen were upgraded several times as design and effects improved it's only reasonable they'd look similar. plus, as i mentioned earlier, i think they don't want to waste their time on a new design when they have a perfectly good one. They're probably going with parallel worlds having parellel designs.
or a wizard did it.

Bow ties are coool.