It being 2011 and all, I'd kind of expect that we'd be able to emulate a fairly simple subtractive synthesis architecture with a reasonable degree of accuracy. In fact, given enough time and effort, a reasonable emulation of [x] using any number of modern tools could be achieved. That's the point of a dedicated emulation, to make your life easier, to save you time and effort.
While the success on sound accuracy is debatable (and a waste of effort, IMO), the argument places all its emphasis on the end point.
There are two debates conflated into one, and that is the problem. On the surface, they ask, can you hear the difference between a simulation and the actual. A valid question, but this is only one of many aspects of that tool in use, and doesn't tell the whole story of utility, yet many people believe it is the only one that matters.
Thankfully, the modular synth won't challenge/response my ass every time I want to move it to a new room ;)
What is your goal? If your goal is to closely replicate the sound of a Prophet-5 preset inexpensively, I'd imagine the Arturia Prophet V (or others like it) to be a useful product.
I suspect though, the real goal for many customers is music creation. There is a huge difference between recreating something that already exists and the process of original creation. I don't personally care how accurate a simulation is. The only thing I care about is if the tool is useful to me.
I'm looking at all these demos of the monome, but I'm yet to see it do something I can't already do. Why bother getting one? I don't get it.
#conclusion You monome people are really weird.
…and there is nothing that can be done with a sampler that can't be done by editing little bits of tape together.
Making music is a process. How well you relate to your tools has an enormous impact on the success of achieving your goals. If you look at the endpoint only and ignore the process, you're depriving yourself of an vital component of the act of creation.

