To be fair, ACB is not just 'slew' or 'slop' between parameters. It is as mentioned above, a wholly different approach than traditional VA.
In traditional VA, you create an oscillator and then use digital methods such as filtering and envelopes to sort of recreate the analog synth using digital approximations of the analog components - they can be tweaked and slopped up, but at the end of the day, they are wholly different as they are built from components that inherently operate different than the analog counterparts.
You're creating a digital filter for example, any way you want, and then tweaking it to sound right.
In ACB (Roland's term for circuit modelling), you go even lower level - you emulate the circuits and the flow of electricity which eventually produces your oscillator and your filter, but again, its a very low level, so it matches almost exactly. Very powerful stuff that is really starting to penetrate the consumer realm.
Contrary to what I read above, I'm not so sure that the VST versions are different, or traditional VA, as this circuit modelling is still software, and so would be reproducible on a computer.
For example, Maschine uses it in it's sampler emulation. Universal Audio stuff uses it in almost all of their emulated software.