Yes, and the centralized version comes from a tree that in the Linux workflow is only able to be modified by one person. You submit patches via email or pull requests (literal ones, to pull from a repository); you don't share commit bits on a centralized repository.
When I install Linux 2.4, that centralized version comes from somewhere.
I agree that svk could have made for a serviceable GitHub, but the fact that Git had such things natively supported is a big advantage.