Calculating the True Price of Software
http://www.onlamp.com/pub/a/onlamp/2005/07/21/software_pricing.html

Lefkowitz, Robert
O'Reilly and Associates
2005

Abstract:

Therefore, the major difference in worldview between open source advocates and proprietary software license advocates is explainable as a differing opinion on the correct value of the volatility of maintenance and upgrade pricing. People who believe that the pricing on maintenance is stable and unlikely to change see greater intrinsic value in the software. People who fear that the pricing is subject to large fluctuations see no intrinsic value in the up-front license; stripped of the options, the license value approaches $0.