I think it gives the illusion of a wider stance on the car, and in the case of the 3 Hyundais posted, each has progresively more fender flare - fenders wider from the base of the body. On the RD, the wheels/fender lip is more narrow than the fender and rest of the body it seems. The RD lines wouldn't be able to pull it off.

 

I think I get what Majik is getting at. For a given height of fender, a higher flat section means that the rest of the fender can have a more aggressive flare.



If these flat areas keep getting bigger...

 

Needs 4_7/8" spacers in the rear.

 

The flat spot on the wheel arch is commonly the widest part of the car's body. They leave the edge flat so that you can park cars closer together.