Ummmm. Okay, yeah...that figure might seem a bit distracting, and while you're right most battles have been fought with more...you also have to take into account that this is NOT an Earth battle. This is Middle-Earth, a battle between Elves+Men and UrukHai+Orcs. Not only are they fighting with swords and sheilds and axes and arrows and torches (which can inflict a LOT of damage...but probably not as much as a gun and a grenade), but they are all supurbly trained warriors. Everytime I saw Legalos in a fight, he moved so fast and so accurately. And remember the scene when Gimli brags about killing two and Legalos was already up to fifteen? That says it all. And then there's the UrukHai, who are basically stronger, faster, a little smarter, and definitely even more brutal than their Orc cohorts. You pit so many skilled fighters against each other, it's going to take them all a LONG time to get to actually killing each other. And besides...10,000 is STILL a lot...as far as I'm concerned, that sounds like a reasonable average number of sodliers for any medieval campaign.
It's a good point, but...it didn't bother me too much. I still think the battle at Helm's Deep was greater than that in "Braveheart" or anything George Lucas can hope to conjure up.

*Note: Oh, BTW...George Lucas is that idiot who's doing those "Star Wars" movies...y'might've heard of him maybe?*