"neither Wayne nor Dianne were wearing a seat belt when the car was removed from the water"
Oh yes, I'm SURE if they had been wearing precious seat belts, they would've been saved from the murky waters.
</snark
I saw a report once that said seat belts absolutely improve your odds in that situation:
(a) You are much more likely to remain conscious
(b) You are much less likely to become disoriented -- helpful if you need to smash your way out, but especially helpful because you don't waste time figuring out where the door handle is and which way is up.