The way they've been able to keep the price low while using quad-cores in EVERY iMac has been by downgrading the GPUs. The Graphics Cards in EVERY model are now mobile. In the last line of iMacs they were full powered desktop GPUs.
So, you see, while there's an upside (the processors), it doesn't come without a down (the GPUs). At first glance I was really annoyed as the £999 one (which is what I got before the refresh) had an i5 quad core, then I saw the graphics memory and got even more annoyed, but THEN I noticed the large shiny M at the end of the GPU name. THAT's how they've been able to bring us them processors and still keep the price down. They've downgraded the GPUs. As my i3 processor practically acts like a quad core anyway and is virtually never pushed to it's limits I think I'm more than happy with what I have. The GPU may only have 256MB dedicated memory but at least it's not mobile.