Some of the people I've met who feel that roleplaying in WoW is strange are the same people who enjoy roleplaying in a tabletop game most. To them, the game environment feels stiff and sterile, lacking the imaginative breadth and depth that a tabletop game is capable of. (Incidentally, there is a tabletop version of WoW also, and although I have not played it, I would one day very much like to try.) Yet roleplaying in an online game like WoW just requires one to apply his or her imagination in a slightly different way, and many of the same basic elements are still the same.
Today, for instance, my Psychic Warrior and his friends in D&D faced down a gigantic crab covered with mutilated corpses that had been hiding under a huge battlefield full of dead bodies. I missed a lot of my attacking rolls, so my character got beat up really bad and actually didn't do much good against the monster, but before and after the battle I had some chances to make everyone laugh with his mishmash of Eastern-European accents and his quirky personality, so I still got to contribute something of value and helped make it a worthwhile experience for everyone.
In WoW, too, although the contribution my character can make in battles is less determined by the luck of the dice (and more by the quality of my gear), in the end of the day the battles in either system are basically just a game, with mechanics being played out according to a certain strategy. They act as a pacing element to give context to the interactions your characters have with one another. The real fun of it comes from playing your character, and enjoying the way other people play theirs. In either format, battles add spice and fun to the experience, but entertaining one another is really what it's all about.
The main difference here is that in a tabletop game, you go through a more traditional story arc: a call to adventure, a passing of various thresholds, and finally a climax in which you may influence the world in some way. In WoW, roleplaying isn't about saving the world, and traipsing through Karazhan each week certainly isn't the same for most people. In my current guild, however, the way we go through such a dungeon is about as close as you can get to a real story experience in a dungeon. The raid leader doesn't use words like "main tank" or "dps," and instead talks about "protectors" and "attackers," and speaks about characters like Moroes, for example, as if they really are doing something (like having a party) and waiting for us to arrive. It's not the same as a tabletop game, for sure, but it's definitely more immersive (and much more fun, in my opinion) than any other raid I've been in.
And creative immersion is really the whole point. Whether in the tabletop RPG books or WoW computer game, all the tools you use are simply focal point for your imagination. For instance, the Storyteller (also known as a Game Master) for my D&D game today made a grid, some special maps, and some small character tokens we could use to move around and get a better sense of where our characters were and what they were doing. Back in high school, when I was the Storyteller, I used to draw on this big whiteboard that was available at the time for the same purpose. The tokens and simple pictures were aids to the imagination, and helped us to picture everything going on even without the aid of a billion-dollar-budget special effects company.
In WoW, no matter how complicated or beautiful our characters are, they're still basically just another form of tokens and drawings. Where our characters stand and what they do all convey something directly to our imaginations, from which we can get a much clearer appreciation for the world, the characters, and the stories they are a part of. Just as some people always prefer imagining scenes from a book rather than seeing them in the movie theater, some will always prefer the old standard of the tabletop roleplaying game for such interactions. But although back in the day people used to say that movies would replace books, the fact is that today both media coexist side-by-side.
Likewise roleplaying in tabletop games and online games will both continue to develop and improve, and many people like me will continue to enjoy both for different reasons. Because when it comes down to it, roleplaying is roleplaying, no matter the medium you choose to roleplay in. What really matters is how your group uses the medium of choice to entertain and interact with one another. The books, table and dice, your avatar, gear, and computer environment are merely aids to help get you going -- the story is entirely up to you.