All I know is that running my fingers across my HHKB Type-S is Soooooo much more quite than my WASD v2. I think a lot of it has to do with the keycaps (thicker PBT vs. thinner ABS).
Neunelfer might also have a valid point. When running your fingers across the keys they will still get pushed down a tiny bit. When the key is pushed back up to its resting spot the bottom of the plunger will hit the top of the case making a noise. By adding dental bands that return noise is lessened as it is now hitting softer rubber.