From my memory of my class of mechanics of fluids, air is considered a fluid.  To get a fluid to flow there had to be a differential of pressure from one side to the other.  In your case it is probably a fan pulling air through the radiator.  The Venturi  Principle would apply.  Each hole would act like a venturi.  The principle of the venturi states that the fluid will speed up as it goes through the venturi and slow down after it gets through.  So in your case, the expanded metal screen will basically not restrict flow at all.

http://en.wikipedia.org/wiki/Venturi_effect