I read on another forum that a failed tail light on an '08 F150 disables the vehicle by design. I have a hard time believing this to be the case. What do you guys know about this?

 

That's hilarious. I've had a tail light out on my '07, truck ran fine.
It would be a bigger safety issue if your tail light went out while driving or in stop and go traffic and the truck becomes a motionless 2 and half ton brick.
In that guy's story, something more was at play. How would the light go out from a car wash? Something else in the truck was damaged that caused his problem.

 

I think what we have here is a cause/effect confusion. The shift lever has a brake interlock on it, you have to press the brake pedal to select certain gears. If the brake pedal position switch fails, you could loose brake lights and the shift interlock, preventing the truck from being shifted out of park. The PCM has no control over the shift interlock.

Edit, Also these trucks do have a shift interlock override, so if he read his owner's manual he would've know that.