Comment 3 for bug 1120870

It's not an issue with any Ubuntu-wide infrastructure: just with the involved packages and their dependencies.

In the case you referenced (bug #260849), Intrepid's photoprint binary package depends on libgutenprint2, presumably because it needs libgutenprint.so.2, but Intrepid's libgutenprint2 package only includes libgutenprint.so.1. The package's dependencies are incorrectly declared, or the dependency broke its interface. This isn't something that automated Launchpad or Ubuntu tools are meant to be able to detect; it's just a straight package bug

Your assumption about what happens when a new Ubuntu release appears is somewhat correct. All binaries and sources from the previous release are copied into the new one, all at once. This means it starts off just as consistent as the previous release was, as it contains exactly the same set of package versions. Things can only break when people upload new packages later on, and those packages have buggy dependency lists.