Not sure there is a strict necessity for "losers", either, if you want to go to positive sum, but claim some gain more than others lose. Situations where in a small world both sides gain (ie no loser) are conceivable.

Edit: I flatly reject the notion that strictly someone's gain requires someone's (non-proportinate) loss, ie that there are always "losers". That notion is also not really a current macroeconomic position.