I'm sorry, but this is for the most part simply not true. A low end CPU will bottleneck your system far easier than a low end GPU will with WoW.
Edit: Oh, and the bit about 90% of PCs from the last 10 years having dual cores is completely wrong too. It was only 5 years ago that they began with the Pentium Ds. They had some meant for servers and the like before that, but those are hardly main stream hardware.