Interesting difference. Possibly due to differences in individual lenses. That is something I always worry about. Unless a lens is really bad how do you manage that?
In one of the comments I recall reading that the 70-200mm lens did not perform as well at shorter distances. Perhaps a difference in these two tests was the distance to the object imaged?
It will be interesting to see what sort of charts slrgear.com produces when they do their detailed test.