You don't see the jaggies and artifacts?

Also, I did forget about the approximation editor but I did adjust the displacement tesselation settings.. Also is your plane a poly plane or nurbs plane as per the example. We are not comparing apples to apples if you are using nurbs. Because in that example they start with a 25x25 plane then go in and change render tessellation 5x5 per spane or in other words turn the 5x5 plane into a 125x125 plane! So you end up with a super dense mesh (see below, see my original post that got flack).

I am going to redo my render with the approximation node. But I stand by what I originally said regarding mesh density affecting the displacement quality. The only thing adding an approximation node does is not mental ray automatically subdivides the mesh and then applies the displacement. So you end up with really high mesh density at render. Which was my argument against displacement in the first place!