I've written before about some of the advantages of open source software, but I have just stumbled onto an article illustrating on key advantage of open source software, longevity.
The article details the purchase of a private anti-virus company by Microsoft back in 2003. This isn't new news, and it doesn't seem like a big deal on the surface, but in reading the article, one quickly sees this anti-virus company produced a platform independent anti-virus solution.
This means that their anti-virus product will run on any platform including Linux, and some saw this move as an weak strategic move to try to stifle the growth of Linux as a viable alternative as Microsoft quickly announced "GeCAD will continue to expand its services and security business and develop new non antivirus related technologies and software solutions."
This meant that anyone using this company's anti-virus solution was out of luck. The product would be discontinued.
Users of proprietary software have no choice but to submit to the will of the CEO's of the respective companies. In an open source product, if a group of users don't like the direction a project is going, they can take the source code and create a fork of the project, or continue to support an older version.
This simply isn't an option with proprietary software. Suppose Microsoft decided to stop supporting Windows XP and Vista, and released the newest version of Windows for $1000.00 a pop? It may not be a likely scenario, but it is a possibility. Microsoft could fold as a company, again highly unlikely, but if the company did tank, it would take all of it's users with it.
With open source, the project will survive as long as there is any kind of community or demand for it.