I don't think that the MOAB killed anyone.

[popeyespappy]

Kinda sorta. The over pressure is the highest when the two waves first meet which is at some point out from but very close to ground zero. Jehanne is right though in that it loses energy the further from that point you get. That being said the over pressure that results from an air burst is still higher than it would be in a ground burst because there is no reflected wave adding to the effect.

Which is why I am wondering (out loud) why they dropped the damn thing in the first place?

Because they expected it to be effective. More effective than trying to get a piece of ordinance inside the cave itself. While setting off a large explosion inside the cave would undoubtedly be more devastating to that cave and its contents it is also a lot harder to do than just getting a great big ass bomb close. Especially when they thought close would be close enough to to do the job.