America loves Bush because he tries to do the RIGHT thing, and in this case, personal expression of sorrow and empathy is the right thing to do. Not only will it gain him votes (and that's not the reason he's doing it) but it will also resonate well with Arabs.
Anyone who thinks Bush should not have expressed this sentiment is overthinking the situation and playing politics. With Bush, heart trumps politics, America KNOWS that, and that's why the guy has 55% of the nation's support.