Quote: "well,newton is free."
Sure, and it's a good free alternative for a physics plug-in. But if you got the money and are willing to pay then Dark Physics will be the way to go. It contains advanced features. Particles(Like BatVink mentioned) and cloth, which can be ripped apart. It's also faster(as I already stated) and therefore, you will be able to calculate dynamic objects in a scene without too much frame rate loss. Dark Physics also contains the ability to use fluids!(Although this feature requires the PhysX card). Then it's also hardware enable(As BatVink stated), which means that you will be able to have even more calculations at once! Which means much, much more dynamic objects in the scene etc... It will also be much easier to use. In one line you will be able to have a dynamic object that obeys the laws of physics. This requires several lines in Newton(Not many though).
Quote: "They will be products in their own right"
Yeah, I agree with this.
-The Nerd