well i guess you are confused
the thing is
ATI is a CHIP making company
i.e it only makes the GPU-Graphics Processing Unit
the chip which is called 9800pro,Fx 5800 etc
while ASUS,Powercolor are companies which buy
that chip and the graphics board format from the company like ATI,NVIDIA
ATI or NVIDIA is diffrent from the Asus etc
asus etc assemble these cards and sell the cards
while buying a card you give more importance to the GPU then the company like ASUS
the best GPU's made are by Nvidia ,ATI etc
hope you get it now