Having read all the previous posts I have some agreement with both sides.
People can be really cruel and make jokes about any disaster, any death, any misfortune, basically anything that is different, this gives the impression that the creator of the joke is a cruel, evil person. But, this joke creator is trying to bring laughter and providing that the recipients of such jokes are carefully chosen and on the same level as the creator, there seems to be no harm done.
Though should the sick joke reach someone directly affected by the unfortunate subject, such as a person who has lost a family member or their home, then that would cause unnecessary hurt. Just to make a point, we could all be affected by the Japan disaster!
I personally don't appreciate such jokes and should I receive one, as a text message, as an Email or even verbally, I would chose to totally ignore it.