For me, the main difference between a (good) sample and (even the best) sythesized sound is easy to define: The sample will always have this certain "built in" musicality --- an artistic consciousness that the player(s) and the producer condensed from the myriad of possibilities into this very recording. You would have to know the Do's and Dont's of _each_ instrument as thoroughly as the highly specialized players from the sampling-sessions to achieve a similar result from a synthesized source. It may look enticing, but in the end you're spoilt for choice.
/Dietz (with his private opinion)
You know, the penny dropped during a conversation I had with Sharmy this afternoon about his recent Synful demo and another one he did using samples. I commented that the sampled violin had a certain life the other one didn't have (other factors aside).
Then I remembered what Dietz said in the quote above, and it dawned on me that this is what he's talking about. It's the same thing I liked about the Spectrasonics Bass Legends library ten years ago - they're alive.
Okay, I get it.