What's at issue here isn't necessarily whether the drop was legal or not. Even if you conclude it was illegal, that doesn't mean he gets DQ'ed. That just means it's a 2 stroke penalty. The issue is the scorecard. You're not DQ'ed until you sign the card (another incredibly asinine rule of golf). I don't think it's unreasonable for Tiger to conclude that his drop was legal, therefore he can sign the card without worry. He knows all eyes and cameras were on him the entire time. It happened probably an hour before he signed his card. He could have reasonably concluded that if there was a problem with the drop, the rules officials would have had time to review it and would have contacted him had there been an issue.
With all these circumstances coming into play, I don't see how it's fair to disqualify a guy from a tournament he's in contention to win.