I accept most of what Greg had to say (at least through LWN's eyes) but there is one thing I would contest:
Then, there is the matter of redistributors who base their products on another distributor's work; these are distributors like Ubuntu or CentOS. There are no contributions back to the community from that kind of distributor at all. They are not functioning as a part of the Linux ecosystem.
CentOS is different than a normal distribution (at least for the core OS) in the sense that our aim is to be 100% compatible with RHEL. That of course means we cannot change anything (except the things we legally have to). Bug-reports and patches go up to Red Hat and we wait for them to be accepted and pour down again.
Now, I don't think CentOS in itself is a big contributor to patches, much like the article already explains why RHEL is not in itself a big contributor. But saying CentOS functions outside the Linux ecosystem is probably one bridge too far and depending how you interpret "ecosystem" it is wrong or intentional :-)