One of the arguments for choosing Apache/BSD/MIT software licenses over Free Software licenses like the GPL is that the former harness the profit motive of individuals and companies for the benefit of the open source users. There is hypothetical positive feedback: Apache/BSD/MIT licenses allow proprietary extensions, which in turn lift up the open source source software by giving back bug fixes and feature enhancements.
Does this actually happen? Is the give-back significant, or does value mostly work its way up from open source community contributions? How many fixes and features come from work on proprietary, pay sites? How many come from proprietary, commercial software products?
I've made proprietary MapServer-based sites -- sites available to paying users, but no downloadable code or configuration -- and when they required enhancements or fixes of MapServer, I made the improvements and then gave them back (with consent of my customers) to the MapServer community. However, most of my MapServer contributions were made through my work on community, for-the-public software. The same goes for MapServer in general: most recent work on MapServer was (i'm digging up the stats on lines of code) done to implement OGC standards (WMS, WFS, WCS, SLD) for public-facing Canadian government web sites.
Do any of my readers have examples -- I'm specifically curious about any involving MapServer and GDAL/OGR -- of proprietary sites or software that have extended and improved open source GIS software?