As I understand it, manufactures work on a points system, so to speak, for how much their vehicles pollute. The more a model pollutes, the higher the number, the less of these vehicles you can sell in an area depending on the population density. They are limited to the points they are allowed in a model year (allthough they can purches points from other manufacturers who dont use all theirs up) They get points kickbacked to them for selling vehicles under a certain emissions limit. This is why GM rebadges Suzukis, Toyotas and Daewoos so they can sell more trucks and suvs.
Anyways, this maybe Porsches reasoning for the smaller engine, the rich guys can buy the, possibly underpowered (we dont know yet) more emissions friendy car for his wife who would probably never use its full potential anyways, so the he can still buy his twin turbo flat six. Just a thought.