It is hard for anyone to claim that Reason has it's own sound quality. It has it's own DSP algorithms and floating point math which is probably different to any other DAW, although I'd say there would be some similarities with Cubase/Nuendo/et al from the Steinberg stable given that Rewire was first created to allow Cubase and Reason to integrate.
Purely from a perceptual point of view, the sound you hear has been altered by your sound card and speakers/headphones by the time it gets to your ears.
So, no Reason does not have a sound of it's own, any perceived differences are down to personal biases that are unfounded in fact.
Sounds like a great PhD research topic - "The Perceptual Inference of Quality for High-End Digital Audio Workstations". Would need to standardise audio interface and speakers and headphones for this to be a viable experimental series.
Oh, and as for sounding shit on your car stereo, ever thought that it may not be capable of what you thought it was???.