<br />The two 2-handed weapons were valued at only 1200 GP each, while the +2 Longsword was valued at 2000 GP and the +2 Gearon's Heavy Mace was valued at 2500 GP (more than double). Even if the 1-handed weapons could be used by more classes, if the 2-handed weapons really are superior in the hands of Fighters, Paladins, and Barbarians, the 2-handed weapons would have been in great demand by those three classes and the prices would have been more equal.'
<br /><br />I'm not sure why you would believe that. If we're saying that the one-handed weapons were basically good for twice as many character classes (and they were) than the two-handed weapons, why wouldn't they be worth twice as much? Even if the two-handed weapons were _THE_ best for the 3 classes they were good for, the one-handed weapons were _THE_ best for three of the six classes they were good for. Everything would point to a good fit value of 2x for the one-handed weapons. Not that priceguide is good for much in cases like this. The accuracy for purps has always been off, often to an order of magnitude. After all, I'd happily buy just about any purp for the equivalent item gold values listed, but I doubt I'd get many sellers.<br /><br />
Since there is such an inequity in price even during a year when there are two of each (1-handed & 2-handed) available, it is clear that even for the classes that could use a 2-handed weapon, the overwhelming preference of players was to use a 1-handed weapon and shield. And that explains why the Dragonscale Shield was worth 3600 GP (well over any other PURP in the set), as it was unquestionably the best shield for anyone that could use shields, and gave extra AC to anyone using one plus a point of fire resistance.
<br /><br />See above.<br /><br />
One of the other arguments you were using for the superiority of 2-handed weapons is that you can defeat the monster and have time left over for treasure or searching the room. I feel that if you have everyone outfitted with the top 1-handed weapons, you will be able to defeat the monster in time to do all of that as well.
<br /><br />That's actually the arguement douglas made, and I hadn't thought of. It's absolutely true though and it might be the most valuable part of two-handed weapons. This was exspecially true in the past as you might recall, as early on dungeon time was a LOT tighter than it is now (and in addition I'm sure it just seemed so as well because of lack of experience which would still have play today for newer people). People took room damage left and right. It was, in fact, one of the major complaints at the time and I'll be willing to wager it's still the major cause of damage dealt rather than monster attack.<br /><br />
Another point you made was that it made sense to use 2-handed weapons if everyone in the party was doing so. That is probably not something most parties can assure. Many times you are going on a TD run with some players you don't know, so you can't know what weapons they will use. Even if you do know everyone, it is likely that one or more people will feel strongly that they want to maximize AC instead of damage. Just like the Prisoners Dilemna - if you use a 2-handed weapon but nobody else does, everyone else benefits by reducing the chance they'll personally get hit and they also benefit by you doing more damage to the monster at no risk to themselves.
<br /><br />Douglas also touched on this. I can agree with that and accept that's why there might be a slight premium. This is usually only a problem, again, in groups who not only don't cooperate but are openly antagonistic to one another. If your group's cleric refuses to heal anyone but himself no matter what and actually refuses to use scrolls you pass him to heal you, you're probably sort of flocked anyway. At that point, more AC is definitely a good idea, though IMO, I keep a cloak of elvenkind and 20 cure minor wounds potions around at all times to deal with those wankers.<br /><br />
It may make mathematical sense for an entire party to use 2-handed weapons, but I think most parties won't be doing that. And, you two might be the only two that have actually looked at it mathematically, most others are doing the intuitively logical (and emotionally satisfying) approach of maximizing their AC to minimize the chance that they will be hit by a monster during combat. The token values (1-handed weapons and Dragonscale Shield being so much higher than 2-handed weapons) prove that out.
<br /><br />I don't believe the values are all that far off from what they should be. We would easily expect the one-handed weapons to be worth about 2x the two-handed weapons for everything ranging from supply to the facts I mentioned above about versatility. I think it's driven by mainly rational reasons, though I will buy into your idea that some people are impulsive and stupid. Not to mention that there's the nostalgia factor. There were no great swords or axes in DnD where a lot of us cut our teeth or even adnd until 3rd ed. If you were a fighter whozit, you always wanted a longsword or a two-handed sword. That certainly carries over to the TD experience.