I would be interested to know what are the other top GitHub repositories. Afaik the Nix package manager uses a similar model (using a GitHub repo as a database), however they periodically release snapshots and the default configuration uses those instead of git.
I'm not sure how DefinitelyTyped works, but their repository https://github.com/DefinitelyTyped/DefinitelyTyped is huge and may be they use that github repository as a single distribution point.