[jamesdsadler]

Git does use diffs extensively its algorithms, just not in its representation of history. Git's "domain model" is blobs, trees, commits, branches and tags.

At a lower layer than that (the pack files) it does use binary diffs to store similar objects as deltas to save on disk space.

TL;DR diffs play an important part in git's machinery at different levels of abstraction. They just aren't part of how it represents its domain model.