The joke was funnier in its original form: Which is heavier? A pound of feathers or a pound of lead? People who weren’t really thinking (or were very young) would choose lead, when the right answer was neither. A pound of anything is still a pound. The size would differ, based on the items compared, there’d be a lot more feathers to make up a pound than there would be of lead. That’s what would make it funny.
The joke was funnier in its original form: Which is heavier? A pound of feathers or a pound of lead? People who weren’t really thinking (or were very young) would choose lead, when the right answer was neither. A pound of anything is still a pound. The size would differ, based on the items compared, there’d be a lot more feathers to make up a pound than there would be of lead. That’s what would make it funny.