I was pretty fascinated by the steep rise of Git's curve. Of course, the statistics are not representative, but they resemble a good set of somewhat typical Debian systems.
Today, I somehow thought about the graph again – and started investigating. Take a look at this graph:
On April 1st, one of the Git package maintainers uploaded a commit that changed Git's package name to "git" from "git-core". In the graph above you can very well see the steep ascend of of the red line ("git installed"), while at the same time a sudden drop of the "git no-files" package occurs. Slowly, the purple "git-core no-files" follows, indicating that APT replaced git-core with its dummy package that only contains dependencies, no files.
This doesn't explain why the red line's ascend is so steep; however, there must be some relation the package's name change.