Keeping the enemy from gaining money is abstract?Except they're not taking them, they're killing them. You have to think of them in an abstract manner for it to make sense - is basically what you're saying here. I mean shit, why not just not send our little minions out with gold in their pockets in the first place?
They're the crux of why though - the gameplay is more approachable due to the mechanical differences, and the other reason is largely the visual/lore aspects. People get attached to character,s they don't get attached to generic units.