The problem with giving back to open source, in many cases, is that the competitive advantage you might gain from adding your own cool customization or bug fixes, is gone because you've now released that stuff to others. That ruins some of the advantage of going your own way.

And if you don't give code back, you've created a fork.

Personally I don't have a problem with someone using Open Source code or the MS platform, or anything else. Just pay for what you use, the base software. Give $50k to the open source project that you used as a license fee or so they can continue to develop more of the same type of software you used.