Now hang on a moment! They are willing to release the results of thousands of man-years of work to us. I would see this as a very generous contribution to a community-based development project for RISC OS. And they did have to pay a lot of money for it in the initial acquisition from Pace.
If other developers want to contribute source to this project, they are likely to be users of RISC OS, too. They will receive new versions of this OS for next to nothing (I think the figure suggested was a few pennies?) and there might well be a clause in the licence, that developers, who's source has been accepted into the project, will get future versions completely free of charge. The commercial developers in the RISC OS market might want to contribute certain changes to RISC OS wich would enable them to release new products through wich they will get new sales (like ADFS-improvements for CinoDVD). Then there is the possibility of user-funded development like the UPP, only for OS features.
Also some of the in-house developments of the STB-developers might be contributed to the "open-source" version.