WordPress.com makes the Jetpack. They strongly push self-hosted sites to use it, especially the Publicize feature. Publicize is how my blog posts show up on Facebook, Twitter, LinkedIn, Tumblr, and Google+.
WP.com also strongly pushes using the composition on their site rather than the one on the self-hosted site. It is cleaner and easier to use.
Part of that cleanliness, though, means features are not as… clear. On my self-hosted site, the Publicize informs me when I need to re-confirm permissions for Facebook and LinkedIn which both expire after x days . The WP.com version, does not show when I need to re-confirm permissions. The “Sharing” options are collapsed and even if expanded do not show the errors. So, basically, posts stop getting shared for a while until I notice and fix it.
One would think that WP.com being the maker of Jetpack would ensure that users choosing to use their composer would ensure they are alerted to a problem ASAP.