^Absolutely. And others have turned such roles down (I earlier mentioned Daniel Day-Lewis and Mortensen himself for Batman Begins, Chris Cooper turned down the role of Gordon in that movie, Sean Penn is supposed to have been their first choice to play The Joker in its sequel).
I'm not claiming to have any particular insight into Mortensen's thinking - I just get the impression that he's not into this kind of movie. But like I say - I'll be quite happy if he proves me wrong and accepts this role.
Anyone know if Viggo is going to do The Hobbit?