Where are the plugins in the source code repository?

Sorry if this question was asked and answered before and I missed it in the forum; or I am missing the bigger picture of core vs module licensing issues.

I was browsing Elgg source code @ http://github.com/Elgg/Elgg and noticed that most of the plugins found in the full release package are not in the repository.

I checked out the source from git for testing 1.7. I also wanted to check out the modules so I can stay in sync with changes that go into git and not have to rely on the nightly packages. Where are these plugins in the repository?

Thanks.