Nick:
No, the protection that I speak of is not only offered when a player is all-in; the player is protected from having his winning hand mucked if and when he tables his hand at any showdown, regardless of whether a player is all-in (Rule 15).
"Everything you say goes against rules for tournament poker". I disagree. I see nothing in the tournament rules that requires the dealer to tell a player, "don't muck your hand, the board contains the nuts" or "don't muck your hand, if you have one card higher than the card X on the table, you will win because your opponent is playing the board". I would not be in agreement with having a rule that the "next to show" hand cannot be mucked if the board contains the nuts, for example. We might as well then have a rule that says "once the board shows the nuts after the river is dealt, the dealer shall declare the hand to be over, no betting actions will be permitted, and the pot will be split evenly amongst the remaining players". This goes way too far, IMO.
Also, if you want to have a rule that requires the dealer to intervene and say "don't muck, the current hand is playing the board", or "don't muck, the board contains the nuts", you require the dealer to be competent enough to recognize those situations on the fly and to intervene accordingly and correctly.... and we know how critical of dealers you are already, why give them more opportunities to make mistakes?
I have seen the following situations occur:
1. Three players at showdown, board is AAA77. Player A shows KJ but Dealer (correctly) says "Aces full of 7s" and pushes the board cards upwards. Player B mucks his cards face-down here, mumbling that his "Q-high" is no good, and C shows pocket sixes. Are you saying that the dealer should intervene and stop the showdown at B, to explain why the (alleged) Queen isn't part of the best 5 card hand? I say muck B's cards, and inform B of his error afterwards if you want, but no advising play during the hand.
2. Board is AKQJT rainbow after the river is dealt, the Ace of hearts is showing. Three players left in the hand. Player A goes all-in, Player B calls. Player C is last to act and asks, "if someone has the Ace of Spades, will that beat an Ace of hearts high straight?" The dealer and TD decline to answer. Player C folds, afraid of the Ace of spades-high straight. Do you think the TD should have prevented C from folding here, and explain why suits do not matter in Holdem? I say muck C's cards, and inform C of the error afterwards if you want, but no advising play during the hand.
I don't have any problem telling a player, "I can't advise you how to play, but I can only read your hand if you table it." But whenever a player chooses not to table his hand, then he risks mucking a winning hand. We want the best hand to win at showdown, yes, but players either need to table the hand so that we all know it is best, or the player needs to learn how to read a board.
We often say that if players want to avoid an adverse ruling because of an unclear betting action, we tell players to verbalize their intentions. Similalarly, if players want to avoid potentially mucking a winning hand, we should tell players to table their hands at showdown. In the infamous words of Nick C here on the TDA forum: "It's that simple."