Stealing someones weapon in combat is definately some variation on attacking objects or disarm, not any sort of pickpocket attempt. A great fighter should have a better chance of holding onto his weapons than someone who can't fight. I tend to favor the disarm rules, but they don't really work.
Pick Pockets doesn't work at all, since the skill is all about if anyone notices you, its not actually taking the object (ie its not a combat skill).
Its not easy to grab someones weapon without grappling them. To look at a modern day situation thats somewhat close, if you tried to say grab a cops gun, all he really needs to do to stop you is put his hand on it. If you tackle him and keep his arms at bay you've got a pretty good shot. At the point its really grappling though.
