Some games use more of one thing or the other. many MMO games hit the cpu harder. This may explain WOW.
A part of this balance is that the cpu feeds the video card so if the cpu runs out of power(because it is working very hard) it can not feed the video card fast enough.
As I said above it works both ways.
You can have a FAST cpu sending work for the video card faster then it can get that work done.
Example would be placing a 4350 in my media center(Something I have done
, If i do not want to game it works ok, but actually is SLOW on the media center interface). I did have that for the lower power/quiet, but it can not play any games with decent settings. The cpu can send as fast as it wants, but the video card holds it back. The same system ran a fair amount of games rather well with a 5770 in it.
With a GTX 650ti in that system, I can get both cpu and cpu to work fairly hard and it is more balanced(A bit more video would not hurt, but come on, its a small system and this card is quiet.).