Tieflings had got popular enough to be a 'proper' player race. I remember back in the 2nd edition (and planescape torment) times when you were doing a tiefling you rolled a D100 to see what you got for their eyes, horns, hair, skin, legs, tail, wings, ect.
I can understand the idea behind a unified appearence; there would be one with the art just to stop people going "What's that supposed to be?" when they see a humanoid with 2 prehensile tails, multifaced insect eyes, digitade legs and leathery wings next to your Annah or Valen or Neeshka, and it can also make things a bit easier for dungeon masters, since it gives them a bit more of a known quanitity to plan around in advance.
