I understand your feelings but legally speaking the only abuse of that kind would be taking GPLed software, modifying it, distributing it and not sharing it back. If the software has been licensed with BSD or similar licenses that don't require to share modifications, then the original developers are perfectly fine with not seeing anything coming out from those corporations. Their choice, no abuses.
Absolutely. It is in their own interest to share contributions upstream. If they don't, they are forced to re-apply their patches over-and-over or just not upgrade.
