The difference is when Bush made the proposal for a 4% annual CAFE increase in 2007, the automakers were in a LOT stronger position than they are today. By essentially "arm twisting" the automakers while in dire financial straits, gets them to agree to almost anything. Not only that, but a lot of California's political peddlers (Pelosi, Boxer, et al) got their way in getting the Fed to standardize w/ what California runs along on.
The funny thing is just a couple months ago, Obama's proposal was lower than Bush's proposal for cars and light trucks, but today, the story's different.
You realize that in order to achieve a 42 MPG cafe average, this puts "performance-minded" as is currently known as, cars out of the picture. Even cars like the 4-cyl Mazdaspeed 3, that's out the door.
Now my big question is this - what should we expect for our older classic cars, as well as the late model V-8 coupe sitting in the garage. Will we be protected by either 1) some sort of "grandfather" clause, 2) a special "collector car" registration process and tax 3) smog laws designed to circumvent collector cars, but targeted at getting the SUV's and early 2000's stuff to the crushers
I envision changes to the smog laws, but how, and to what extent, is still unknown.