Based on the way the game is run according to the books. I can't account for every possible subsystem used by DMs in what I'm saying - which is that there is no mandate for hiding this information.
Very true. I just am all in favor of things that emulate "fog of war" - which what we call any kind of flub, miscalculation or forgotten action at my table. "Worse things have happened in the heat of battle," we say.
Perfect example from 2 sessions ago, one player thought another had cast
protection from arrows on him, so he yelled at got the attention of a bunch of spear-wielding barbarians from up on a roof, and when they threw four at him and I told him the damage he turns to the other player and says, "Now how much does the spell absorb?" the other player replied, "What spell?"
Turns out the spell cast on the PC was
message! The wizard had cast protection from arrows on two others and there was just some confusion about who got what. What did we do? We didn't take it back. . . We just rolled with it. . . In the frantic preparations for the barbarian attack there was a poor assumption made - it made for drama and a funny confrontation after the battle.
To me this is the essence of the level of immersion I am looking for in my games.
Plus, playing the way you described would cause combats to take longer than they already do, with questionable benefits
Yeah, never really worried about the length of combats, and the benefit is the fun of imprecision
Anyway, I have found that allowing people to count things out before they do them (in my game, if you count out boxes for character movement you have moved that way, no take-backs (on the other hand I do warn players about potential AoOs as they approach them)) leads to slow downs where folks try to figure out the exact perfect way to move and try several possibilities before choosing one.
Heck, we even severely limit suggestions between players unless it is in-character (allowing intelligent enemies a chance to hear and react).