As a console, the idea is to reduce manufacturing costs with the newer tech. At the same time, heat and power consumption are reduced. Clocking the smaller chips higher is possible, but is absurd for the console arena where everything should be equal (if at least for the sake of Q&A for games) and where the normal-clocked chips would be in higher abundance. i.e. "Who would want to buy the crappy edition?"
In reducing the transistor size, there are some redesigns in the chip to make it optimal, but there won't be any fundamental changes or additions.