If you select to only view stable packages in the Online Package Database it happens to see some unstable or masked packages, too. Example: http://packages.gentoo.org/daily/2006/10/03/archs/x86/stable/ As I've added http://packages.gentoo.org/archs/x86/stable/ to my news feed that's a bit annoying.
I don't see any "unstable" packages. The links you provided show that all packages are x86 stable. While there are a few of them that are hard masked, and I have no idea why a maintainer would mark something as stable *and* hard masked, the output on the pages appear to be accurate, showing only stable x86 packages and marking whether they are hard masked or not. Sure we could filter out masked packages, but there will always be another to come along with a bug report saying that the page isn't listing all the stable packages.
