and i stand by what i said. no resouces are going to these leaves, thats why they are deteriorating, resources are leaving them. did you know that something around 50%(not exact figure but close) of light passes through leaves? so really theyre not blocking as much as you would think. they might no longer be powerhouses, but the are still sinks for valuable resouces. thats why they drop when gently tugged, the plant has finished pulling availible resouces from the leaf and it had started to dry out.
and as for the plant not having adapted a better way in nature
...c'mon, its had millions of years, i think its got it down.