i'm not going to argue that some of the new software doesn't sound really good, because it does. but i don't think the cpu power comparison says it all.

with digital hardware there can be different ways of implementing the synth. some digital hardware uses the exact same philosophy as a computer, with a strong cpu doing most of the processing, and the rest of the electronics just providing knob inputs and such, and of these kinds, i think the comparison is fair. but there are also digital synths that have a more analog philosophy, using more descrete parts. they might have a smaller/slower cpu, but dedicated dsp chips and custom made ic's for different functions, giving them all the power they need, and making them harder to replicated in software.

i know that my sampler from 1999 is like that. it's cpu is noticably sluggish and you have to be patient when changing screens or loading samples, but the circuit board is covered in dsps, and it has enough juice to play 128 notes with 72 filters, 72 eqs, and 6 reverbs. my 2 year old P4 couldn't run that many plugins to save it's life.