Apples and Oranges
Porsche and BMW are, in comparison to Maserati, mass market cars.
In the first half of 2005, BMW sold 145,000 cars (including Minis) in the US, Porsche sold 16,000. In ALL of 2005 Maserati sold 2100 cars of all types here. Worldwide sales were only 5600.
If I take a drive of any length around the Bay Area, I'll see at least 100 BMWs, probably a dozen Porsches (including the occasional Carrera GT) and frequently a Ferrari, Bentley or Aston Martin. I've only encountered another Maserati on two occasions.
In addition, it's hard to distinguish an M Series from a regular BMW (or IMHO a Saab, Volvo, Lexus, insert other boxy sedan here).
Porsche, although I love them dearly, aren't much better stylistically. Ever since the 993 they've been moving more towards the amorphous blobby styles of Nissan, Toyota and Mitsubishi.
On the other hand, Maserati retains the classic long hood, short deck of the classic sports car (think Ferrari GTO) It's far prettier than either the Porsche or BMW.
Finally there's this exchange from "Gone in 60 Seconds"
[in a Ferrari dealership]
Memphis: Roger, I have a problem...
Roger the Car Salesman: Yes?
Memphis: I've been in L.A. for three months now. I have money, I have taste. But I'm not on anybody's "A" list, and Saturday night is the loneliest night for the week for me.
Roger the Car Salesman: Well, a Ferrari would certainly change that.
Memphis: Perhaps, Mmmm. But, you know, this is the one. Yes, yes yes... I saw three of these parked outside the local Starbucks this morning, which tells me only one thing. There's too many self-Indulgent wieners in this city with too much bloody money! Now, if I was driving a 1967 275 GTB four-cam...
Roger the Car Salesman: You would not be a self-indulgent wiener, sir... You'd be a connoisseur.