"Am I wrong, or would a criminal only have to pick up his casings to foil this new law?"
You're right, but I don't see a lot of drive-bys coming back to police up their brass.
Having gone to high school in LA not all that long ago, I can tell you that some of the driveby artists saw this one coming.
Instead of leaning outside the car and shooting their weapons at full arm extension, they'll simply keep the gun inside the vehicle and use the car as a brass catcher (which is what some of the brighter ones were doing as early as 92). Assuming they care at all, that is.