Secondly, retrieving the original weapon is going to both use up action resources (minor/move/standard/minor & move) as well as more than likely leave the character open (granting combat advantage). To my mind, this is a significant penalty. A savvy group of players should be able to take advantage of a disarmed NPC.
I guess this is where we differ. I find that to be a pretty lame penalty. Like trip, except worse, and with a greater likelihood for unclear rules outcomes. And in game terms, its an effect that is kind of disconnected from the logical purpose of disarming someone- the most practical effect of the "move action to recover" disarm solution is to make disarming someone into a way to slow down their movement. That's not really the point, is it? You want to disarm someone so that they're unprotected and you can kill them at your leisure, right? It kind of turns disarming into a weird form of tripping.
I'm ambivalent on the whole "sure, you can disarm a bear" thing as well. I guess I don't find tripping large monsters that unrealistic, so those analogies don't work on me. You knock the dragon's leg out from underneath it, it scrabbles back to its feet. Ok. Same with tripping a gelatinous cube. You knock it off kilter, it bounces back into position. Whatever. And on top of that, while its constantly ignored on this forum, its worth remembering that the rules don't actually give you carte blanche to do those sorts of things. The DM has explicit discretion to disallow uses of powers that don't make sense. He's encouraged to come up with ways for power use to make sense wherever possible, definitely, but that isn't the same as declaring that anything goes.
I think the basic dichotomy I set up describes the problem.
If being disarmed is a major sanction, it should be very tough to do. If its a fight ending sanction, it should be just as difficult as reducing someone to zero hit points. The easiest way to accomplish that is to declare that it actually requires reducing someone to zero hit points.
If being disarmed is a minor sanction, it shouldn't be so tough to accomplish, which means it will happen more often. But then you have to worry about whether its turning into a farce, and whether players will figure out workarounds to turn it into a game ending sanction yet again (I disarm him with an encounter power, you push him a space with an at will, now he can't get his greataxe back, and the high level solo NPC barbarian is completely screwed out of all his best abilities). Plus, you have to figure out all kinds of rules for how your foes fight while disarmed.