Did you know that even the software that this blog runs on is open source? Yup, WordPress is developed by the user community. Other popular blogging platforms that are open source are Movable Type and Livejournal.
The advantage of this arrangement is that it puts power into the hands of the people who are most passionate about it. Is that someone who uses the software, or programmers being paid to work 8 hours a day? Of course users who will ultimately benefit from improvements to the software will be more passionate about it. That is one of the reasons why open source is here to stay.