I wonder why things should be so active. There are lots of moons around, suggesting lots more traffic in the area than my naive expectations, so maybe Pluto took a big hit not too long ago and it's still relatively warm inside. Maybe it managed to grow around a core with some heavy metals, and the thorium is keeping things moderately toasty. And maybe there's some squishy ice clathrates that can be toothpasted around a little easier than the usual rocks--though I'd expect that they'd fall down quicker too, so maybe not.
It's a shame the probe couldn't have carried the extra weight of fuel to slow down and orbit a while. I hope some of those images due back in the next year carry enough information to get some spectral analysis of the surface rocks. (Reflection only tells about the very top layer, but that's better than nothing.)