When 10.04 (lucid) was released we added "Supported: {5y,3y,18m}" tags into the Packages file that is stored on archive.ubuntu.com. This was needed because the individual packages get a different support time based on the "seed" they are in. The server packages are longer supported than the ubuntu-desktop packages etc. The additional information makes it trivial people to check the support status of a particular package and also allows scripts like "ubuntu-support-status" to work.
For the upcoming 12.04 the timeframe is changed compared to lucid. The desktop packages are also supported for 5y and there may be architecture changes. The current code in LP is not flexible enough to handle different set of rules for LTS releases, it expected that the rules are all the same. This branch fixes this by adding a UbuntuMaintenance class that can than be used to extend for LTS releases.
The QA I have done on this to run:
$ python launchpad/trunk/cronscripts/publishing/maintenance-check.py lucid > /tmp/lucid-old-code
$ python launchpad/maintenance-check-precise/cronscripts/publishing/maintenance-check.py lucid > /tmp/lucid-new-code
$ diff -u /tmp/lucid-old-code /tmp/lucid-new-code
(and the same for maverick).
Fixed in stable r14623 <http://