Cliches abound in fantasy literature. Elves are long-lived and lithe; dwarves are stocky and bad-tempered. Humans are usually prone to corruption, but there is always one boy who just may be the hero that will grow up to save the world. Fantasy role-playing uses a lot of clichés as well. The mage is squishy and needs to be protected by the burlier fighter. The duel-wielding drow swears that he's nothing like the rest of his foul people. The paladin who is literally holier-than-thou. Beyond character, there is the cliché that all adventurers are out looking for loot and that dungeons are full of monsters guarding said loot. Upon further reflection, some of these clichés are necessary for good fantasy roleplaying and some are just useless. The ones that work are mechanical, while the fantasy clichés that are purely aesthetic are just overused and need to be thrown out.
Mechanical clichés are what makes fantasy roleplaying function. Removing them would require an immense amount of house rules and tweaks and I am not convinced that doing so would always end up in a better game. One that is discussed in this week's issue of The Escapist Magazine is that every fantasy roleplaying setting is post-apocalyptic. In order to have dungeons and ruins populated with monsters that guard treasure the likes of which hasn't been seen for generations wouldn't be possible unless there was a technologically or magically advanced civilization that had somehow been destroyed.
Look at all of the classic fantasy settings of Greyhawk, Dragonlance or Blackmoor, and you will note that each had some form of Atlantis that had been wiped out of existence, but had left behind wondrous items of magical power. These are the items that player characters are always happy to collect. An apocalypse sets up the basics of fantasy rolepaying so brilliantly that you'd be hard-pressed to play a game that didn't have some post-apocalyptic themes running throughout. Of course, that doesn't mean that some people won't try.
The idea that a player character starts off fairly weak and grows slowly in power over time is also integral to the idea of role-playing games. The examples in fantasy literature are easy to spot. You could say that Sam, Merry, Pippin and Frodo started out as 0-level commoners and that they gain experience throughout the course of the Lord of The Rings. Merry and Pippin became fighters (I'd say up to level 5 or so but that's up for debate) while Frodo and Sam might have duel-classed into thief for their sneaking ability, finally reaching demi-god status and epic levels by traveling across the sea into Valinor.
Leveling up in role-playing games takes the abstract idea of getting more powerful by seeing the world and defeating monsters and makes it concrete with the concept of experience points. Killing the Witch-King on the fields of Pelennor gave Merry at least 3000 XP, maybe more. Without the mechanical cliché of slowly gaining power, there wouldn't be much of a game to role-playing.
Roles in the party are also a necessary mechanical cliché. The physically weak but mentally strong wizard is as common a cliché as you can get, but without the inter-party relationship that such a cliché provides, there would almost be no reason for parties of adventurers to team up. If Marcus the Amazing could take as much of a beating as Falco the Brave, then why in the Seven Hells would he bear having such a weak-minded fool around? The whole idea of a group of characters, each specializing in a certain sphere of expertise, is a cliché that spans all kinds of genres, from fantasy to superhero groups in comics, to even the A-Team. Without the band of merry adventurers, fantasy roleplaying isn't that much fun.