Most software is priced like a disposable commodity item on the iPhone because it is a commodity. You haven't developed your own distribution channel, and you haven't developed in any software 8 other people haven't already made, so your software is not worth much money per item. Those with difficult to reproduce software like navigation systems companies can charge $50 on the iPhone, quite successfully.
A candy bar costs $0.50 and each one has to be physically manufactured, distributed, and occupies retail space. But that's not a bad business - Mars Co is incredibly profitable. Pricing is an optimization problem, and there's no moral issue here. You are free to charge whatever you like; some prices make you more money. It sounds like World of Goo has made a good deal of money selling their software for $20, and managed to make a good deal more by offering a temporary sale (much like a department store). What's wrong with that?
A candy bar costs $0.50 and each one has to be physically manufactured, distributed, and occupies retail space. But that's not a bad business - Mars Co is incredibly profitable. Pricing is an optimization problem, and there's no moral issue here. You are free to charge whatever you like; some prices make you more money. It sounds like World of Goo has made a good deal of money selling their software for $20, and managed to make a good deal more by offering a temporary sale (much like a department store). What's wrong with that?