The debs on the Elasticsearch site are links to Github downloads: http://www.elasticsearch.org/download/2012/12/07/0.20.1.html links to https://github.com/downloads/elasticsearch/elasticsearch/ela.... If you don't have a reflex to check the destination of a link to a binary you might not notice it that much, but I see a decent number of projects hosting their release builds on github. It's certainly common for APKs as was pointed out above, but I've seen it for Adium plugins, debs & rpms, even full apps - if memory serves the precompiled SSHuttle gui for OS X was hosted on github as well as the code.
Plugins are managed (quite nicely) via GitHub downloads. This includes official and third-party plugins. The official plugins can migrate elsewhere, but it will be difficult for the third-party plugins.