That's a good idea and probably what I'd do if I were to take it one step further - in particular if you went with null item drops, it would be great to "subclass" that so that its ratio does not interfere with the rest of your calculations. I.e. - 1:20 chance of dropping an item, 1:6 chance that it is item type XYZ.

+1 for Diablo 2, the game that destroyed my grades in school. :)