[CentOS] RHSA-2012:1288 libxml2 security update for centos6 skiped?

Thu Sep 20 12:05:38 UTC 2012
ownssh <ownssh at gmail.com>

I saw libxml2 have a security update on
https://rhn.redhat.com/errata/RHSA-2012-1288.html.
But centos only update libxml2 for centos 5., it also affect centos6.
Centos already update ppid(RHSA-2012:1269), looks like
libxml(RHSA-2012:1288) skiped....
Any explanation?