Originally Posted by TheDefiniteArticle
You're wrong about the others. There's no need for both to show at any stage - you must only show to claim a part of the pot (for which all cards must be shown). AFAIK this applies equally to cash and tournaments, but etiquette dictates that you do show to speed the game up. Of course, you can invoke IWTSTH, but that makes you look like a royal *******.
In tournaments cards do need to be turned up, although I'm sure some tournaments can make their own rules. This is from the offical TDA site -
11: Face Up for All-Ins
All cards will be turned face up without delay once a player is all-in and all betting action by all other players in the hand is complete.
I don't see anything specifically about the river.