Pretty sure the adreno 320 has 4 cores as well. The die size on the adreno 320 is much smaller though hence why it can be used in phones. The powervr gpu in the ipad 4 is gigantic. The battery is also gigantic to compensate. I added a photo to my previous post with benchmarks from my nexus 7.
True the iPhone got the tri-core version since the quad-core version cannot fit.