I've been trying to refrain from getting into this, but I suspect that the dumping of the body was done for, yes, a variety of reasons. But I suspect that one important one is that he wasn't killed in the firefight itself:
Obama wrote:
Today, at my direction, the United States launched a targeted operation against that compound in Abbottabad, Pakistan. A small team of Americans carried out the operation with extraordinary courage and capability. No Americans were harmed. They took care to avoid civilian casualties. After a firefight, they killed Osama bin Laden and took custody of his body.
Emphasis added. From Obama's speech last night.
Now, maybe that's just more semantics. But they worked on this speech for a long time and actually delayed it. Hard to believe that's not what they meant to say. Not "in" or "during" a firefight, but, after.
Strikes me that they didn't want an autopsy done even within 24 hours, so they wouldn't find powder burns on the back of his head. I dunno, maybe not - it's not like they were going to go out of their way not to shoot him. Interesting that no one's really asking about this aspect of it, though. Seems like they didn't want to go to a trial or have to keep him in custody (capturing him alive), and this was the easy way out. Get rid of the body, and you don't have to answer those questions about why he didn't come back to stand trial.
Honestly, though, I, too, was surprised that there was no body to display. You'd think that would have been integral to announcement. In fact, I thought that perhaps this had been done a few days ago, and they were waiting to get the body back to the States or something to make the announcement.