The Nefarious Part
When I said that further examination seems to reveal a lack of nefariousness in General Petraeus' non-inclusion of actual numbers alongside his graphical representation of the numbers, I didn't mean to imply that there's nothing nefarious at all about his presentation. As numbers-maestro Ilan Goldenberg points out one major source of difference between the Petraeus numbers and the Pentagon numbers is that Petraeus has taken the US casualty data that, according to Petraeus, is the best available and blended it with Iraqi data that everyone regards as unreliable.
Why would you want to do that? Well, because it helps bolster the argument Petraeus is trying to make.