Some of those guys spend big money and know what they're doing, which isn't the case with most car stereo shops.
Luxury car manufacturers pay close attention to car acoustics and stereo component layout especially on their premium stereo option. I'm willing to pay for the factory upgrade and get much better sound, vs having the typical car audio hack put aftermarket crap in my car. Even the more expensive aftermarket gear can't compete with a quality factory system that are tuned to the car's interior by acoustics engineers.
