Yes, the charges are on the ticket, but wouldn't you want to know how an officer came to the conclusion that you were in violation of some law? Its everyone's legal right to request disclosure. This may appear to be a loop hole, but if the prosecutor is doing his job correctly, then there would be no loop hole to exploit.
What if there are witnesses at the scene of the incident. Would you not want to know the contact information for who gave statements to the police and also have a transcript of what was said or have the ability to interview a witness yourself? <-- Or would you rather find this all out during your trial?
There are 3 reasons you would want disclosure of the evidence against you:
1) To prepare a good defense
2) So you are not surprised at trial concerning any new evidence that might pop up.
3) If the prosecutor believes he does not have a case to convict you, this will be shown with in the disclosure material.
This is the reason why everyone needs to make notes of what happened when they receive a traffic ticket. Everything needs to be noted including the description of the police officer.