Basicly they are very pessimistic on depletion itself (the percentage for the world in general lies very high near 10% at the moment (type I + II + III) if you look at WEO 2004). And very optimistic on the depletion curve!

Another thing is that they are still way optimistic on discoveries, maybe you should note the amount of discoveries they are counting on from Saudi Arabia... (and the entire world, its USGS again!)

And they are less optimistic on reserve growth then in the 2004 report...

Could you use the word "decline"?  Sorry, it's just a pet peeve of mine.  Depletion refers to the percentage of reserves produced, while decline refers to an actual decline in production.