Thats the first time I've seen that info, the vents in mine areEverything I've read and all of the pictures I've looked at showed this is the way they should go. However, on these rotors in particular, direction doesn't matter as much since they are straight vanes. That's when the main concern on direction comes into play.
http://zeckhausen.com/how_to_properly_install_rotors.htm
straight but the rotors from PowerSlot were stamp with a L and R
and I remember the instructions said install drivers side L.
Been running this way for +30k miles with no problems.