First off, Movies like Grease are not "Car Movies" So one must be careful by what they consider a car movie. Some movies have lots of cars, i.e. "Dazed and Confused", but that is not a car movie and the cars are merely props to give it some feel for the era being represented.
Second, something that would be a "Car Movie", i.e. Cannonball Run, are usually made with current vehicles to represent that period of time. Only in historical situations, like Tucker, does close enough really count and some attempt is made a getting it right.
The lamentations in the Grease thread about it the movie not being correct on the vehicles is not far off, but then again, it is not a really a car movie, it is a Musical about Teenagers, set in the 50's, and to the casual movie goer, it looks right. Mission accomplished for the movie makers. And for the accuracy types, it is a travesty!
So those are my thoughts, you mileage may vary.