Strange trend with GPU and CPU combo

[Zucker2k]

Then why are the roles reversed with Radeons if its simply IO and CPU-GPU communication ?

Good question! Poor answers tho, unless you want to believe that AMD writes bad drivers for its own platforms, etc. For now, the phenomenon can only be explained as follows: in bottle-necked scenarios "... Nvidia's card cannot translate the Core i7's microarchitecture into the same performance advantage, giving AMD's Phenom II-series chips the advantage...." - Tom's Hardware (quoted from link above).