Mmmmmmm... In GNU, there are differences between what a distro understands by stable software and the upstream understands by stable software. Gentoo calls unstable (in some cases they mask the packages) a lot of software declared as stable by upstream, eg: GNOME 3, FFMpeg 1.0, Amarok 2.6 and 2.7, GRUB 2...
In Sabayon, they import the packages and end of conversation. If it works (compiled with sucess and without problems with dependencies), the packagers put at weekly independently if the software is alpha, beta or final release. Or in many cases, Matter does it automatically.
Also, considering the number of package (2.6.90 in case of Amarok), the Matter doesn't detect it as beta software. The same happens with Opera and Wine, for example.
PS: Amarok 2.7 is in the Main repos. Probably it will go to weekly in the next saturday.