I don't really understand why... Aside from the GPU, there was nothing really outdated with the previous models. I mean... the new models have barely changed. Intel didn't even have much in the way of more advanced processors lined up for this. They tacked on two cores, and they charge an ungodly amount of money for it. That's about it.
While it probably won't make much of a difference in the 4/6 core lineup since the six core model will likely be priced quite high (Probably $2999-$3299), really high end users who can really use the high end 8 core models will likely prefer to get the high end 12 core models.