As I mentioned in "What are the basic ClearCase concepts every developer should know?", ClearCase might have some "decentralized" features with its multi-site repos, but it still a CVCS at its core:
it has a strong link with system user-id (which isn't relevant in a DVCS, where there is no unique user referential).
it has a unique repo for managing label and branch names (admin vob), while you can define a 'test' branch in 15 different Git repos without problem (except you need to know what repo1/test stands for, relative to repos2/test).
it also centralize a merge workflow definition through the (UCM) Stream hierarchy (you can visualize where you are supposed to merge a work from one Stream to another).
it proposes through UCM a definition of subset of codes (component), with dependency management. Git only has submodules, without override/overridden detection mechanism.
it manages any kind of files, even large binaries, while a DVCS (any kind of DVCS) is better off managing only source code.
The bottom-line (in our migration from ClearCase to Git) is that it involves quite a few refactoring/reorganization of the source code in order to have manageable Git repositories.
