> An overexposed digital picture may have no recoverable detail, while an underexposed film picture may have no recoverable detail.

There's a further nuance here... that depends on whether it's negative film or reversal (slide) film. Overexposed negs are better than underexposed, as you say, but the opposite is true for slides. People who shot "chrome" films would often underexpose by, say, half a step, while the opposite was true for those who shot negs.