Commons is spread across many Drupal.org projects. The initial intention there was to make it easier to re-use components of the distribution inside other distributions, and to assemble sites with specific sections of the distribution. Where possible, Commons is architected to avoid dependencies (eg, Commons Radioactivity alters views defined by other modules to add a Radioactivity sort when it is enabled, thus preventing folks from having to use Commons Radioactivity if they don't want it for their site, Commons Profile Base is used in COD and has roughly 1.5-2 times the number of reported installs as the Commons distribution.).
One drawback to this approach is that it can increase the complexity of contributing to the distribution. For example, amitaibu pointed out that requires several patches to implement or review a single issue.
So, which components shall we move into the main repository?
I propose we start with all of the content type modules and the landing page modules, though am certainly open to establishing criteria or a general rule of thumb to figure out which components belong where.