Some already do. On Northwest it's a $15 upgrade if you've bought one of the cheap tickets.
I fly quite often and usually "post-business hours" (after 1700, red-eye flights, etc.). For the amount I pay, I expect to be able to utilize the functionality of the seat I'm in.
I was asked by a woman once to not recline my seat. I politely informed her that she would have to pay me $25 -cash- (the cost of an upgrade) and I would gladly oblige.
She didn't and I recline and snoozed all the way to Houston.