AaronOfBarbaria
Adventurer
This is a case of their not being a "standard way" of handling things....is revealing the foes current Hit Points supposed to be the standard way to play?
However, I would note that the game rules are not being changed by interpretation going either way on this matter because the game does not outline a rule that information must be shared, nor that it must be concealed (and the DMG doesn't really suggest either course either). Which means it comes down to a preference: players being able to make informed decisions about when to use particular options, or players having to rely on guesswork to make some options work (whatever the reasoning behind either might be).
I personally lean towards letting the players know when their character's stuff is worth using, as I see nothing gained by trying to prevent the players from knowing the game-rule and how-stuff-works side of the game that we are playing - because it is a game, and I insist on treating it like a game (and in case I haven't said 'game' enough to make sure the implication that too many folks forget the 'game' portion of 'role-playing game' and try really hard, in vain, to make it serious business: game).