I don't get why people keep complaining about this. The Core 2 Duo are still very solid, very capable chips. Given the tough situation that Apple was put in by the new licensing/chipset restrictions on the i series processors I think the decision they made makes the most sense for the people who would typically purchase the 13" model. You get a decent CPU and a GPU that'll be useful for casual gaming and even more useful when more applications adopt OpenCL. This also allowed for better battery life as the i series parts are known to actually reduce battery life when compared to C2D counterparts.
As far as Apple's ambiguity regarding the i series chips I think you are looking at it wrong. The 13" would have most likely received an i3 CPU which would have been a minor speed increase at the cost of graphics performance and battery life. The 15/17" models use i5/i7 CPU which is a more considerable performance boost hence the marketing for it.
Sure I'd have liked to see an iX in the 13", but given the restrictions I, for one, prefer the Core 2 Duo w/320M and better battery life. I'm very glad I waited and didn't buy last month.
First off, please no one attack me for this statement. Anyway, I agree, i dont understand the enormous amount of complaints. Me and my friend went to the apple store and i got a 13" and he got the 15" with i5 and honestly, when we did comparison tests with different apps, the differences in speed of webpages and apps are minute. Maybe a 2 or 3 second difference and a little larger for programs like photoshop. If you cant wait 2 or 3 seconds, i might question why?
He can play more graphic strenuous games, but i will take amazing battery and portability over that anyday. If i want to play cod, im going to my xbox on the big tv, not my mac.
Though it is last years tech, i think core 2 duo is still very relevant. Heck, my family bought a dell (bleh, hate windows still) with a pentium processor and it runs pretty fast too. I guess im just not techy enough to understand all the hooplah surrounding these chips. Though i can say that prices shouldve gone down on the 13" for the upgrades it got. That is my only complaint.