Because it's not warranted. As it stands, the older generation would only run it "as well" if they were clocked similarly, and this is because the architecture is relatively on par. Since WoW really won't make use of the additional cores, you're right in the sense that it probably would be better. Anandtech echoes this. HOWEVER, you're wrong in stating that AMDs can't run/have compatibility issues in World of Warcraft.
Also, before saying no other benchmarks exist, do PROPER research.
http://www.anandtech.com/bench/Product/147?vs=118
And please, try to be a bit more personable.