Common programs like a web server, or a mail user agent are installed on most computers and have a very large user base. Knowing this, many gifted programmers feel obliged for this kind of Free Software - they just need it for their own and they know to make a difference to the world. So one finds a fast, growing community around Free Software packages that have a widespread use. For specialised software in general and particularly for biological software, one needs to first explain what a particular software does. Often the developers get their satisfaction not from the software but from the excitement of extra insights in biological processes - the beauty of which is likely not to be accessible to regular software enthusiasts.
As a view shared by many in Open Source Bioinformatics, Ewan Birney of the EnsEMBL  project stresses Open Source to "ensure scientific progress". He also laid out that the Open Source of programs is a comparatively trivial issue when compared with the openness of biological data. The latter is often far more expensive to produce. While giving the data away might possibly diminish one's competitive advantage, the sharing of a program with others and respective citations is well accepted as fostering one's career.
Andreas Tille 2005-05-13