Job's moral outrage caused God to appear, thereby demonstrating that the sufferer who believes is never alone. Job abruptly stops complaining, and - in a prosaic happy ending that strikes me as tacked on by other sages so as to get the troublesome book accepted in the Hebrew canon - he is rewarded. (Christianity promises to rectify earthly injustice in an afterlife.)
Now, in regards to the tsunami: maybe it's just my crazy atheist reasoning, but I think it'd be better if God hadn't caused a giant wall of water to fall on several hundred thousand people, even if most of them got to go to heaven. Presumably, they're going to heaven because they're good people, not because of the giant wall of water thing. If you get something you were going to get anyway, it's not exactly a reward.