In Europe a large fraction of new cars are sold as employee leasning cars. The tax regulations e.g. in Sweden mean that it's only viable to pick an environmentally friendly car, which is basically a CO2 emissions value. As an example the treshold in Sweden is 120g/km.

Almost every manufacturer have 2 liter disel models that (just) barely come in under 120g/km, including several VW models such as the Passat. So while a slight increase in fuel consumption might not be much, it could be a huge blow to european sales: if a Passat jumps just a tiny bit in consumptions, CO2 emissions are likely to stray above 120g/km meaning sales will effectively be cut in half (assuming half the buyers of new cars are those who need to get under 120g/km)

To illustrate how tight the margins are, the current model of Volvo V70 with the 2 liter "D4" diesel has offer a special 120g version with 16" wheels in because the standard 17" wheels would be an inch wider, and the resulting increase in drag makes the CO2 emission value 121g/km!