Open Source systems benefit from the many enthusiastic developers/developer groups who continually work on them. They tend to evolve to the better with each fresh idea or talent brought to/joining the development cycle. This is not the same with $$$ software developed by closed, small groups of developers (usually always the same group of people for each system). You might be interested in the following paper on Open Source systems, which describes how Open Source systems have reached a stage of maturity, sophistication, robustness and stability, and usability and user friendliness rivalling that of commercial, proprietary products.