I think due to the fact they are ventilated and softer than the ones in the 400 they tend to develop creases sooner and wear starts to show - The cream leather ones show wear and dirt alot more than grey and black ones. Having said that regular maintenance will prolong the life and condition of the seats - mines are grey and after 135k miles show only a few creases and thats if you look closely - I regularly clean and feed mine with Gliptone leather products.
On the same note the interior plastics are of the best quality you can get - the steering, gearknob and interior door handles still look immaculate with a nice matt finish once cleaned.