no plates... i'm positive it was a paparazzi issue. while im not certain the extent to which the paparazzi pursued steve, the paparazzi around west los angeles (and probably los gatos/silicon valley too) do know the license plate number of cars that celebrities drive. i see them regularly checking cars in the parking lots of restaurants and nightclubs hoping to find one that belongs to a celebrity so they can swoop down when they come out. almost any evening at the ivy you can spot them specifically checking license plates. for a while paris hilton was driving the same car as me (f430, no plates either) and as a result i regularly got swamped by (severely disappointed) paparazzi as i got out of the car. having no plates does throw off the paparazzi, especially if your car is not particularly unique, ie sl-whatever amg mercedes, which are a nickel a dozen in any affluent area. around here the paper-plate mercedes seem to outnumber the state-issued-plate mercedes.
oh, and about avoiding taxes and registration fees..? no, you still pay your fees and such every year, you just don't fix the plates to the car. yes, you do just keep them in the trunk.
steve wasn't being a scofflaw, he was just well-informed. (and yes i did have to edit that to be 'past-tense') bottom line, california law says you have 6 months to mount the plates. swapping out cars every 6 months... i'd say he's earned it.