AT&T/Western Electric's cords were originally designed with the ground pin oriented sideways, so that regardless of the ground pin orientation, the cord would simply exit to the side. I still have quite a few of them on the shelf and use them for this very reason.
Believe it or not, they allowed those cords to be called "light olive gray", along with cable jackets. It was just the cable pair color that was called "slate". This was to alleviate having to use two-letter abbreviations as much as possible.
I will say that I am starting to see this orientation on plugs from other manufacturers as well as "wall warts". All of our cell phone chargers are horizontally-designed. I have also noticed some GFI's on cords equipped with a short leader cord on them so that the GFI is more "in-line" with the cord. I think that's a fantastic idea.
