This raises the interesting question of what is better. To pay $4 per year or to buy out the obligation for a higher amount. To buy out it would have to be an amount which compensates to make up for what would be lost in the future (how do you even calculate that). To pay in advance for X years creates a problem as well. Hard to forget to pay every year, harder to keep track of something that needs to be paid every 20 or even 100 years. Excess paperwork overhead.