It used to be common knowledge that western gamers didn't care for RPG's. They were too slow for us and there was just no way a western gamer would read text when we could play some action game. Then FF7 (first Final Fantasy to be released in EU) proved that if you make a good game people will play it even if it has a lot of text. 
 
It also used to be common knowledge that girls did not like games. Now we know that girls do like games. The SIms, WoW, Farmville, Singstar etc are all games with large number of female players. The reason why girls didn't play games before was that the games weren't interesting for them. The few games made for games were usually garbage and anytime a garbage game for girls failed they saw it as proof that they didn't like games instead of blaming the game for not being good enough. 
 
It also used to be common knowledge that people on the internet did not have the attention span to watch a video clip that was more than 5min long. Then Giantbomb came along and showed that if you make the content compelling enough people will watch 30min quick looks and even 100h endurence runs. 
 
So my point is that even though people say that MMO players don't have the patience to read quests much less listen to them I believe that the reason is mostly because quests in MMO's are so dumb that there is very little reason to. If you have played one "Go and collect 10 wolf pelts" you have pretty much played them all. The millions of copies of Mass Effect 2 sold proves that it's not just RPG players who enjoy a good story, even shooter fans like the game and if a very traditional RPG like Dragon Age can manage to sell a few million copies like it did, then I'm sure Star Wars The Old Republic won't be a flop. I don't think it will outsell WoW or anything crazy like that, but I think the focus of voice overs and a compelling story will prove to be a profitable one.  
 
It's easy to say that no MMO player care about the quest text when there is barely no quest text worth caring about. Just as it was easy to say that girls don't like games when all they had to play were some badly put together horse games.