Except the way that their law is written, simple lack of conviction does not equate to tow and impound charges being returned. The law states that return of costs will be made if there is a determination by the appeal process that the cop ordering the impound and towing did not have reasonable grounds to do so. It also states that the a person may appeal to the police or to the courts, which is the same as saying that the appeal can be outside of the trial process.
In effect, they are talking about returning costs in cases of malfeasance by a cop, and not trial aquittals arising out of reasonable doubt or insufficient evidence to support a conviction.
Which is still a lot more than we have.