Cordain's assertions are based on modern game species, not Pleistocene Mega-fauna.  Larger animals have far greater fat levels than the small game compared in his book.  He also did not include (high-fat) water fowl which would have been common on the Steppe-Tundra.  Cordain admitted to these failings on the Paleodiet List ( not this list).  His work at Colorado State University is also $upported by the U.S. government which strongly encourages recipients to recommend low-fat.
 
On temperate grasslands, vegetable foods are unavailable for most of the year.  On an all-meat diet one must consume at least 61% of calories from fat to avoid protein toxicity.
Even in tropical rain forests, high fat insect grubs and high fat nuts make up a major part of apes calories during the half of the year when fruits are not available.
see:Knott, C. 
"Changes in orangutan diet, caloric intake and ketones in response to fluctuating fruit availability." 
Int J Primatol (1998).19: 1061-1079. 
 
Ray Audette
NeanderThin.com