This is enlightening--
After reluctantly handing off my keys to the car wash guy the other day, I noticed he had some trouble moving the car. From the outside I had no idea what he was doing, but the engine seemed to shut off for a few moments. After some wild gesticulating, I heard the car start back up as it lurched forward.
When I asked him what happened, he said (with conviction) that Jeeps don't move unless the driver's seatbelt is fastened. I've tried to test since with this with no success, by the way.
At the end of the car wash run, a different guy got in to move the car over to the post-wash area, and he struggled too. The car revved up before lurching forward out of the active beltway with only a moment to spare.
When I got the car back, the seatbelt was still fastened (and creased from being sat on). The experience overall left me confused.
This thread sheds some light on what I think actually happened.