Rails 3.1.2.rc2 just got released. Around the time of the 3.1.1 release, there was also a relatively evolved release process including announcements and release candidates.
Minor releases (e.g. 2.x) and major releases (e.g. Rails 2 and Rails 3) usually add tons of features and, even in minor releases, often include major refactoring of some parts to improve performance and reduce code complexity. Both features and major refactoring can introduce new bugs, so release candidates are offered to users so they can help with development by testing their applications on the upcoming version.
But point releases (e.g. 3.1.x) don’t add features or change too much code, they just try to have bugfixes. Bugs are fixed by adding a failing test and making it pass, while ensuring the rest of the test suite passes too. This means each point release has less bugs than the previous one. Upgrading to the newest bugfix release is quick, safe, and should be done as often as possible.
In other words, bugfix releases are cheap. Why waste time with release candidates when we can just get 3.1.2 right away? Then, every fix that would otherwise be made between 3.1.2.rc2-3.1.2 can just be released as 3.1.3.