the mailing lists page should include links to mailing list archives. gmane.org or marc.theaimsgroup.org provide archives for many lists including gentoo.org's. The link for gmane.org might be http://news.gmane.org/search.php?match=gentoo . For marc.theaimsgroup.org I'd suggesting direct links like http://marc.theaimsgroup.com/?l=gentoo-dev http://marc.theaimsgroup.com/?l=gentoo-announces gentoo.org could also provide it's own archives but who needs to reinvent the wheel for the thousends time?
http://www.gentoo.org/main/en/lists.xml has an archive section now. I consider this bug fixed.