Damn. I wrote up a very nice response to this and computer froze. Here's the frustrated version with poor attempts at copying lost wording:

It sucks, but the SB's hand is dead because this can be used as collusion.

To clarify, imagine that the tournament is on the bubble and SB shows a hand that let's BB know that the odds he's getting are slightly low. If BB folds here, it's usually a +EV play for both SB and BB, which means that the rest of the players in the tournament lose equity because SB showed his cards.

Since the floor can't distinguish between the example I just gave and this situation, the floor has to deal with them in similar ways--by killing the hand.