Difference being there could be a time when I couldn't afford a hundred dollar dinner and then time when I can afford it. But a cup of coffee, not really sure if there will be times when I can afford and not afford it.
It's an experiment on social contribution, if I'm correct. Even though you can leech (and some will), a good amount of people might ultimately add more money than they spend from it. But why? Everyone is anonymous (kind of), and it's not like you have external pressure to be good.
If the amount on the card stays positive, you may have renewed my faith in at least a portion of mankind, Jonathan Stark.