And you think that's ok?
Sure. Why shouldn't it be?
Nobody said the officer's estimate is unimpeachable, or iron-clad. It simply meets the intial burden of proof for a prima facie case. If you, as a defendant, have better evidence to the contrary, you'll probably beat him.
I'm surprised this needed a court ruling, frankly. I thought this was already the case pretty much everywhere.
How do you suppose speeding was prosecuted before radar guns were invented? Radar is better evidence, but certainly not the only kind.
Officer testimony is used in court all the time, for all sorts of offences. Why should speeding tickets be any different?