Since ACKS was published, there's been ongoing confusion as to whether thieves can wield a one-handed weapon with two hands. With an errata-fixing reprint scheduled, I'd like to clear this up.
The following text would replace the language on p23 for Thieves:
Because of their need for stealth and free movement, thieves cannot wear armor heavier than leather, and cannot use shields or true two-handed melee weapons such as great axes or polearms. They may use any missile weapons and any one-handed melee weapons. They may fight with a one-handed weapon in each hand, or wielding a one-handed weapon with two hands ”
Yep! I could see some literalists going “Well, this means that they can’t fight with just one one-handed weapon in one hand”, but it definitely makes it clearer to me.
That language is clear to me. As long as we’re looking at two-handed weapon errata, though, I think there are a couple of other points that should be clarified:
Does a character with the Fighting Style (Two-handed Weapon) proficiency only get his damage bonus when he uses a strictly two-handed weapons, such as a great axe, or does it also apply when he uses a standard-sized weapon, such as a battle axe, in two hands?
Is a staff a strictly two-handed weapon that deals 1d6 damage, or a standard-sized weapon that can be used in one or two hands for 1d4 or 1d6 damage, respectively?
In the Warlock thread, it was ruled that, because the Warlock gave up the two-handed weapon style proficiency in return for a custom power, he can only use a standard-sized staff in one hand for 1d4 damage. That contradicts the ruling in this thread, which states that two-handed weapon proficiency is not necessary to use a standard-sized weapon in two hands. Unless using a standard-sized weapon in two hands without the benefit of two handed proficiency is one of the benefits of having Fighting 1 instead of Fighting 0, or is one of a Thief’s custom powers, then a Warlock ought to be able to use a standard-sized staff in two hands just like a Thief can.
That’s not really the ruling in this thread, and I think you’re conflating two things (fighting styles versus weapon proficiencies).
The thief and nightblade did NOT give up their two-handed fighting style. They are only proficient with one-handed weapons, but may still fight in the two-handed style. The warlock traded away its two-handed fighting style, and so gains no benefit from wielding a weapon in two hands.