Why would they do something this silly if they did not have something to hide? Einstein's brain has been preserved for science. Lenin's body was embalmed and is on display in a mausoleum in Red Square, Moscow. Maybe Osama bin Laden is not quite as famous or influential as either Einstein or Lenin, and you would not imagine them building a mausoleum to display his body, but you would think that they would not be so hasty to dispose of the body? And in such an irreversible way. If you bury it, you can disinter it later, if necessary. But when you commit something to the deep, you wave goodbye for good.
So the only reasonable conclusion is that this "burial at sea" was staged and either
- bin Laden is not dead or
- they did something so gruesome to him that they don't ever want the body to be seen. Maybe they tortured him brutally and now are wanting to avoid scandal or reprisals?