Been away for a while...
As you mention 3351, it is not a crime not being able to tell whether a sound comes from a hardware or software synth. Also I agree with the statement that every synth has it's own characteristics: No synth sounds exactly like another.
More than that, I think nobody, not even a "trained ear" can hear the difference between a hardware and a software synth, if he doesn't know the characteristic sound of both the synths.
In other words: Software synths have evolved to match the sound quality of hardware synths (that is, if the right computer hardware is being used).
So, my problem lies here: Why would I still spend so much money on hardware, while I can achieve the same with much cheaper -and much more compact- software?