http://www.anandtech.com/tradeshows/showdoc.aspx?i=2868

A lot of people here prefer consoles for gaming but gaming hardware/software is usually created for PC first and is then used with consoles afterwards. So if our bran new 360 is to truely take advantage of having three cores the PC market has to make some innovations first. As dual and Quad core cpus start to become the norm in the PC realm, PC devs will start to learn how to use them and make middleware for multithreading.

I found and interesting article that talks about this and why having multiple cores is significant.