Bill Brenner published this quote in his story Sourcefire IPO could fuel Snort, users say:
The infrastructure to support Snort isn't cheap and Sourcefire isn't flush with cash, said Richard Bejtlich, founder of the Washington, D.C.-based consultancy Tao Security. "The money to keep Snort thriving has to come from somewhere, and an IPO could give Snort more legs," he said.
I based this thought on the following from Sourcefire's S-1, listed under Risks Related to Our Business:
We have incurred operating losses each year since our inception in 2001. Our net loss was approximately $10.5 million for the year ended December 31, 2004, $5.5 million for the year ended December 31, 2005 and $2.9 million for the nine months ended September 30, 2006. Our accumulated deficit as of September 30, 2006 is approximately $40.3 million.
It looks like Sourcefire's losses are narrowing, which points to future profitability. My point is that development of Snort and associated software (RNA, etc.) takes significant resources. While it might not be that difficult to fork Snort and maintain its code base, adding significant features and developing complex rules would be extremely tough for a noncommercial enterprise to sustain.