They are legally bound to contribute their modifications back to Linux (if they distribute them), it may be a different matter when they don't have to. I can't

They are legally bound to contribute their modifications back to Linux (if they distribute them), it may be a different matter when they don't have to. I can't say I know either way, however I do recall their Tizen SDK licensing not being accepted as open source due to it only granting the right to use certain components on 'Tizen Certified Platforms'.