Casualty ratio

Here is an interesting question.  What do casualty ratios have to do with determining whether an army or nation wins wars or not?  I bring this up because there has been some discussion in the literature abut the fact that in both World Wars the German army achieved kill ratios of at least 2-1 against their enemies yet still managed to lose the war.  Niall Ferguson and John Mosier are the biggest proponents of these numbers.  The crux of their argument is that economies win modern wars not the actual fighting man.  I suppose you could say they propound a material theory of war conclusion.  They really enjoy throwing numbers around.  for example, numbers of tanks, aircraft, ships produced.  Or tons of steel, tons of Coal, tons of wheat produced.  They essentially contend that Germany was simply outproduced into defeat.  There is some weight to their argument, but my personal feeling is that the reasons for the German loss are much more complex than that although relative economic size certainly played a part.