I don't have a technical argument offhand, as my understanding has built up over reading and some use of Csound. My main source has simply been my ears in listening to demos of both Csound and Supercollider and me finding that most of the Supercollider stuff all sounded the same and quite digital. Although I like it, I think Pure Data actually has the same problem. I would wager it simply boils down to the synthesis algorithms used, and Csound definitely also has a huge library of those. I have also seen some examples of Csound being used to synthesize via physical modeling. But I am still getting into all of it.