Git was built to replace a proprietary branch-centric (or merge-centric) versioning system that the kernel devs had used previously, because none of the other available systems were suitable (including several DVCSs, which must be branch/merge centric due to the nature of distributedness).

Also try looking into the history of the DaggyFixes idea (that a bug fix should be committed against the earliest revision to contain the bug and then merge into the active branches, rather than committed against current head).