Sweet. Jesus. That's the most stupid idea I've heard in a long time, have you seen the public lately? You'd essentially be distributing money based on what the media thought was most important at the time, and to whoever could organise the best lobbying.
At least if you charge for individual pieces of software then you can be sure that people will at least (for the most part) be putting their money into what they need over what they want or what they think they want.