Osama bin Laden talks about "defeating the Great Satan for the glory of Allah and Mohammed (pbuh)" for the same reason George Walker Bush talked about "spreading Freedom and Democracy": because it resonates with his intended audience, convinces them that he has similar thought-processes to them and is representative of their interests, or at the very least their team, not because he actually believed that that was what he was doing.

There is a problem with arguments of the form, "The leader of that group clearly doesn't 'really' believe his own rhetoric he's just saying that because it resonates with his followers." This implies that their followers actually believe that stuff, otherwise there would be no point in the leaders' saying it. But you've just admitted that there exist people who really believe that stuff, why is it so absurd for the leader to be one of those people?

The only part I would leave out of bgaesop's paragraph is the "not because he actually believed that that was what he was doing". All of the previous stuff fits fine when both the leader and the intended audience are sincere homo-hypocrites. That is why he is doing it (or equivalently the fact that they do it so well is what made them the leaders). What they believe about the matter can be orthogonal.