Honestly, i think you have to blame the +Buy mechanic for this. If you could just buy as many cards as you liked, you could pick up two $2s instead of a $4. In Dominion, you first need to play a card that allows you to do it, so often $4/$3/$2/$0 is the same to you.
Obviously somebody is going to say this wouldn't work with cost reduction and $0 costs, but man, those are conclusions, not premises.