Why do Windows and Mac send data to the printer in different orientations?

I haven't noticed this until I read this article: http://www.wikihow.com/Print-Double-Sided

It has different instructions on loading the paper back into the printer to print on the other side for Windows and Mac.

Does this mean that Mac prints backwards? Why can't they both print the same way, so they're compatible with each other? Or is it another one of those copyright issues (close, minimize, and maximize buttons on different sides)?