The main reason for this being is because we're on a very tense issue that a lot of islamic people think we are at war with islam. This is another way of showing that we are really not.
Bin Laden wasn't just some outspoken religious or political figure. He was a man who, along with his followers, attacked our interests on multiple occasions, killing thousands upon thousands of our people and our alies. With all do respect to the rest of the world who is concerned about this, get bent. We don't owe Bin Laden the courtesy of a proper burial. If people can't understand that, then maybe they should be the next target.
Regardless, what's done is done. His body was cleaned, properly wrapped, and buried within 24 hours, in accordance with the Muslim religion. I don't like it... but hey, at least no one can say we didn't take the high road.