say Zed released Mongrel under a BSD-license, then any big company (or any person really) could come in and modify it, make it better and then sell it. And Zed

say Zed released Mongrel under a BSD-license, then any big company (or any person really) could come in and modify it, make it better and then sell it. And Zed would be left with nothing. That's what GPL is for, adjusting it is fine, but you can't make money out of a redistributed modified version.