With apt-get and yum you're installing pre-built binaries. This works well if that's all you need to do and are okay with the versions that are installed (typically not the latest unless it's a new distribution).

Once you start having to download and build source for apps/libraries that aren't pre-packaged you can run into issues about version compatibilities, where files are located, do you need to download additional packages (*-dev), etc. Having a service that takes care of this for you solves a lot of headaches (part of why rayburst got built in the first place).