WSOP rules say your hand will *not* be killed if you expose...although a penalty may be incurred if action is still pending (see rules #6 and #34).
http://www.pokerpages.com/pokerinfo/...wsop-rules.htm
Since the action ends with you and your decision to call the all-in, I don't see why you would be penalized. In this situation, exposing your cards will not affect another player's decisions on the hand. I think what you did is fine. That said, it could come down to a TD ruling (which can be arbitrary or biased or flawed), so I'd probably not pull this stunt very often.
BTW: the last B&M tourney I played in, I had an all-in calling decision heads up on the flop...the all-in player jokingly offered to help, so I showed him my hand (an open ended straight)...that's the only time I'd ever done that at a casino... I saw no problem in showing my cards at that point...it was in the spirit of playing, and lessened the impact of getting busted (only had 5x BB, so I was probably going soon anyway).
Cheers,
Frank