A thought about this matter - voluntary payments *really* scare modern corporations. You're pretty much destroying the underpinnings of a consumer society, that being you need to keep buying stuff. Economics is always about ways to deal with scarcity, and with modern information distribution methods, scarcity doesn't exist. Economic models start failing when that happens, so you have to introduce scarcity into the system (copyrights, copy protections, etc.) to have your economic theory work.
Possibly more important, alternative economic systems (i.e. the ransom model) have an inherent upper limit to their profits. Once the ransom is paid, the product becomes free information - there is no chance of breakout hits that make a lot more money than anyone thought they would. You start cutting heavily into the profit margins of a company when that sort of thing becomes commonplace, so you're going to see the record and movie industries fighting this sort of paradigm change tooth and nail. That being said, is cutting into the profit margins of these types of activities a bad thing?
Another problem with that sort of paradigm is that it requires an existing market and user base for it to work - someone has to already want your work before the ransom would be paid. Not sure if the rpg market is large enough to support that sort of thing.
