Manufacturer cars have to be set up so that anyone can own them, and take all the rubbish that Joe Bloggs may throw at them.
E.g. Low octane fuel, poor servicing, thrashing from cold, longer servicing intervals, clutch and transmission life, CV joints etc.
Also its to stop lower models competing with expensive ones, such as the mk4 golf and TT, as well as the R32.
Sometimes the only difference between models is the map, BMW do this quite a lot.