You know I agree with you. I remember seeing a documentary in 3D years ago and unlike other films where you remember seeing something about it, that one gave me memories. The kind you have of places you've been. It was really surprising afterwards even though it wasn't mind blowing during the screening.
So clearly it's PR and everything but I wouldn't say it's bullshit either...

Problem is 4mpg doesn't mean much. Is that 4mpg starting from 15 mpg (26%) or 4 mpg starting from 45mpg (8.9%). mpg gains diminishe as you go higher and higher, meaning that going from 15 to 17 (+11% efficiency) mpg yields a greater gain in efficiency than going from 45 to 49mpg (2x the mpg, but only a 8% gain in efficiency).