in this case it was about having the background pixels black versus white since the foreground text is white. the black contrast on white is easier on the eyes than white on white and that is where the graphic design optimization lies.
we programmers face the same dilemma when a page gets rendered optimally by the back end code or when the code is cleaner and more readable by another programmer, except we look at it from a different perspective and when both the graphic and code design get looked at from the 30,000ft bird's-eye view (the biz) there is no difference: the same output.
there is a difference in the graphic design, but not quantified in bits or time, yet still appreciated, and this difference in graphic design, IMHO and probably backed up by hard stats, would lead to more attention span to the detail when put in front of thousands to millions of users.