I agree there are two ways of looking at this. Partridge wants to be sophisticated, suave, cool and so drives the lexus to give off this impression.
Or the second way is that he is a typical person who drives the IS200 and is a good reflection of the brand.
Personally I think Partridge is always trying to better himself and make people believe he's the main man and so he uses the car as a tool to accomplish this.
Do you think the general public or prospective buyers think Partridge is a typical owner or that Lexus is what Partridge is aspiring to be??