In a 540i Taxi ???? I know sby who has a 540 and if a taxidriver has that, he will banquerouted ! He must have a gazoil 5 series, a 520d, 525d or 530d : there are many in Europe because of the price of the gas !
The S-Class are good sold (many in Paris, but not in the "poor" parts !). The new serie 7 starts well. But again, people who have these cars will use smaller cars (the best example is the Audi S3) to drive in Paris and suburbs : more "fun" to drive, more agility, and in Paris you have to drive not slow, not like in the US, that's a big difference.
An example to end : my neibours have an Audi A6 Avant, a Z3 and a Peugeot 206 S16 : they use the Peugeot to work !