I think Apple perhaps could have went dedicated gpu but then they probably would have put an i3 in the 13" MBP instead of the i5.
I think they decided i5/HD3000 was best bang for the buck over the i3/dedicated gpu given what their customers do with their machines, the price, battery life, internal space and heat management.
That theory makes sense...
I guess there's no choice but to wait and see how those machines actually perform...