It looks like the pencil tool has to be purchased from their store in order to use it - However I've taken a look at some of the samples.
The main difference between their tool and the ArtRage tool is probably that they're not doing live adjustment of the pigment stroke based on a canvas texture, rather they are adding a fixed texture to the stroke so there is more internal control over the result. Because ArtRage is simulating a physical surface the pencil will interact with whatever texture is provided underneath it. You may find that the paper you are using has a particularly fine or rough grain that's adjusting the results.
It also looks like their pencil has opacity control (possibly based on velocity, hard to say without trying it live). Because we're simulating a real pencil we don't provide direct control over digital properties of the pixel in that regard, but if you try taking the softness of the pencil up and reducing the pressure value to simulate a lighter stroke you should see some variance.
The two applications are very different, and there are bound to be some properties of one system that the other lacks, but by looking at the properties of the surface and tool in ArtRage you should be able to get a good range of natural pencil textures that reflect the canvas you're working on. Hope that helps!