Nvidia is why there hasn't been a die shrink to 22nm yet. Sony wants to combine the Cell and RSX onto one chip and Nvidia isn't working with them. You can bet this is why Sony is building a pure AMD machine this time and having one chip from the outset.
This lack of a reduction is also why there was no price drop with the super slim. The RSX is a lot cheaper to make now, but Sony is not happy with the rate of the price reduction.