It is because with the 4870x2 Caldera HS that had the fins in the direction you asked for they had people like myself asking for the other direction so we could mount a fan at the end of the board and blow the hot air out the exhaust slots. This also helps those of us without a side fan or any desire for one to properly cool the card as I couldn't fit a fan between the top of the card and the side of the case. This way if you have no side fan you can easily cool the card by either puting a fan at the end suspended from the top of your rig or just lay one on top of the HS and it would blow down all the cooling fins.

If you have a side fan just get some spacers and put a 80mm fan blowing down into the fin channels redirecting your cool case air into the channels.