Well the air quality is far better. I don't remember if there were any smog alerts this last summer, but in the late 60's and early 70's it was all summer, plus, the number of people and cars is much higher now than it was then.
A lot has to do with geography too. There's always a breeze in the Bay Area and the smog just blows away, like it never existed. LA on the other-hand is a bowl opening to the ocean so the pollution gets trapped. Same goes for Phoenix.
Oh that law. I guess if you bought a '76 or newer TA thinking it would be exempt some day soon, you would be pissed off. I never thought the State would let people start taking their catalytic converters off so I always knew I'd have to pass.