Honestly??? Transmissions just don't go bad one right after the other like that. I work at a dealership too...and it just doesn't happen.
Don't wanna call him a liar or anything....but seriously if they all had that problem, there would be one HUGE recall.
You gotta realize...a dealer has to have suspicions when a car comes in for FIVE transmissions within 50k miles.
I'd be looking into some issue with the car itself...be it a PCM problem with transmission settings.
Perhaps Dave would be able to shed some light on the subject.