The trial is nearing if it's going to happen, and the question remains. Was it legal for the cop to stop me?

Last year I was pulled over for a 5200 cvc violation. Driving without DMV issued license plates. Just to recap, the car was newly purchased (8 days prior), and had the dealership issued paper plates, and registration card in the front window. The officer stated that there were no other violations for his reasoning to stop me. I was not speeding or swerving or impeding traffic. Subsequently I was arrested for refusing to take a breathalyzer. In court, the judge had both sides stipulate that the vehicle was registered at the time of the stop, and in California it is unlawful to pull any individual over simply to check the validity of their registration. If convicted, this case would set precedence, and would allow officers to stop any new vehicle purchaser without probable cause. This is a direct violation to the 4th amendment. Shia Lebouf the transformers movie star was arrested for the same offense six days after I was arrested, and his case was dropped due to lack of evidence. He did not even lose his license. He also refused to take a breathalyzer. He even rolled his truck during the accident! His case was dropped September 2008, and now a year later, I'm setting up for trial. If neither of us took breathalyzer tests, and blood test were never performed, why am I still fighting this case and he's off chillin in the Bahamas?