I thought that the issue here was that the Policeman believed that the rider was going to have an accident going that fast so stopped the guy before he was able to do a full speed check. I recall that he advised the rider that he was travelling somewhere between 2 different sppeds [eg.90-96]. This would have made a prosecution impossible IMHO. Why he didn't just follow and get an exact speed is a different question and was really subject to the Police driver's knowledge of road conditions, problems ahead and so on.
Yes, the Policeman may have been sympathetic but he seemed to act in the best interests of the public.
What amazed me was the rider's assertation that he was not speeding, merely travelling at the speed of the traffic! Like the Policeman said, no one overtook the rider and there was no one travelling at the same speed as the rider, so where did this claim come from - and why did the motorcyclist think it was OK to ride 'with traffic' going +20 MPH over the national speed limit?