Ubuntu is now planning to change how it works with quality assurance process for next Ubuntu release: 13.04. They plan to create a more streamlined, continuous development for future versions of Ubuntu Linux, but they removed the alpha releases and will have one Beta release only prior the final release.
In most Software Engineering terms, Alpha is intended for private testing conducted by the team, while the Beta is more like a public testing. While i can agree that they removed the Alpha release since they can do it in their daily jobs and also by the use of automated testing, but what i can't understand is that they will have only 1 Beta release and no RC releases at all?
Beta release is the first public release. This means, that ordinary users will have their first chance to taste what will next Ubuntu release would be prior deciding whether to upgrade or stick with the current version. With the habbit of introducing new and big changes on every releases, Ubuntu is taking a big risk (IMHO) for Ubuntu 13.04. Less release means less feedback from the users and you know what happened when you can't satisfy your users? They will leave and pick another distributions that works better.
By the way, Ubuntu is now dropped to third popular distro based on Distrowatch's HPD index. The second position is now taken by Mageia, while the top position still LinuxMint. I think by the time Ubuntu 13.04 gets released, they might be overlapped by Fedora.