I (and the GMs I game with) do all the looking up. I've considered having the players look up the attacks on their own copies, but I would have to reveal the DB and AT to the players as well. As PeterR stated, it may not be 'just robes' the NPC is wearing. There could be a magical ring, a spell in effect, actual armour under those robes, or some other thing the PC wouldn't have knowledge of just yet. To help speed things along, I do have the copies of the weapon attack tables so I don't have to constantly flip pages and I can pull out the crit tables that are most likely to be used so things do move along faster. It's not that I think it would make meta-gaming easier, I have really good players who do their best not to, I would just have to reveal too much of what's behind the curtain.
Even the Movement/Maneuver table would reveal too much to players if I set a particular difficulty and the player wants to know why it's at the difficulty that it is. I definitely do not want to reveal the specifics of the crits to the players. I'll say "You hear a sickening crunch as your hammer connects with his ribs. He is visibly dazed and having a heck of a time trying to breathe" But I won't reveal that the NPC has broken ribs, is at -75, stunned for 8 rounds, unable to parry.