Titan anomaly

At www.sciencedaily.com/releases/2012/07/120720103543.htm … a bit of a dilemma. Rivers have been found on Saturn's moon Titan – but something is missing. Evidence of erosion by those rivers, a prerequisite of geological science. What does this imply? The surface of the planet is remarkable smooth with little or any evidence of erosion. This is the burning question in a paper at the Journal of Geophysical Research-Planets. Titan is thought to be 4 billion years of age – created when the solar system formed. Why is the surface younger than the moon itself? One way of looking at it but the kind of problem thrown up by Cassini in its search of Saturn and its moons. What does it mean?