I heard it was a bigger power draw so that's why they went with the lesser chip. The battery also can't be any bigger due to the compact design so some things suffer for the good of the cause.
I'm betting the battery will be the weak spot on this and we will get a good idea how bad once it gets into users hands. Another thing is there are 2 batteries so it is balanced with one in each half. I further read that this prevents the battery from being as efficient so again we'll see in the real world tests by real people using it on a day to day basis.