I don't mind story tie-ins. I think books/comics/whatever that take the game story and expand on it are awesome.
I have a problem though with major story events only happening in a book/comic/whatever. The entire weird zombie event from Stormrage when it was sort of a last stand in Azeroth against sleep zombies while a few brave souls fought the Nightmare in the Emerald Dream? Yeah...no one knows wowgold that ever happened unless they read the book. And that could have been really cool too.
Magni becoming fused with Iron Forge and Cairne dying off screen illustrate this too. Major lore figures should not be killed off in a book! That said, I'm not sure how this could better be resolved in-game. I am thinking maybe with questlines...but not everyone likes quests. Cut scenes might work...but not everyone likes them either.
I can't even watch most of them because I play on a mac and cut scenes tend to crash my wow client so I have them disabled. (They have not worked properly since Cata started.) At the moment it looks--in my cheap wow accounts totally biased opinion--like most of the cool Horde lore happens in the game while the Alliance story gets pushed to books.
This annoys me because some of the WoW authors are so bad I can't read their books. I could not finish Wolfheart because it was so terrible for me--just not the style of writing I enjoy at all. So sell wow accounts...even though Varian was cool in it, I did not see it. I guess what I want most is a more even showing of the story. It would be nice if the bare bones events from all the tie-in media showed up in-game. I would like to see the basic story while I am playing and then go to the books etc. to see it in depth.