I just started working for a small SaaS company that uses open source extensively, and I'm of two minds about this. On the one hand I agree that we are "standing on the shoulders of giants" or perhaps "freeloading" by using this software to support a proprietary solution. On the other, this is far from glamorous SV software development - it's run on a little more than a shoestring and the product is fairly small and reasonably priced, so in a sense, we're using open source to serve customers very productively by focusing only on a narrow solution for them.