The problem is that customers don't understand the possibilities well enough to pay on commission. Right now, software companies are forced to dump a ton of money into a product, and then use the finished product itself to educate users of the benefit of the product, at which point they can begin selling it.
In a "well functioning market" buyers would be aware of what sort of product could be built with what sort of development time, and would pay for the work. (I think this is what's happening with Minecraft - the people who bought the Alpha see themselves as funding its development).
While I bought Minecraft with the understanding that it wasn't done and I was helping support Notch as he continued to develop it, it's not a practice I'd do for a non-game product. I've spent well over $13 on games and had them turn out to not be fun, or only amuse me for a few days. If Minecraft didn't pan out, I've barely lost anything. If it turns out well, it will be more than worth the money.
Were it something important that I needed for my job, or were the cost less negligible, there's no way I'd throw a bunch of money at something and hope the inventor/developer/designer finished it adequately. If someone walked up to you and said "I'm going to build an electric car to compete with Tesla Motors, give me $80,000 and you can have the first one" what would you tell them?
EDIT: Kickstarter too. I've invested small amounts of money in things that I think are worth supporting, with the hope that they get finished well. But I'm not counting on it. It's a risk vs reward analysis that I'm willing to try, but only on small scales.
In a "well functioning market" buyers would be aware of what sort of product could be built with what sort of development time, and would pay for the work. (I think this is what's happening with Minecraft - the people who bought the Alpha see themselves as funding its development).
My take on it, anyways.