[CentOS] automatic import of rpm keys

Hi, I read
http://www.stigviewer.com/check/RHEL-06-000008

The CentOS keys live in /etc/pki/rpm-gpg and when I run yum the first time I am asked if I want to accept the key. Alternatively I could import them manually with something like 'rpm --import /etc/pki/rpm-gpg/$key, maybe in the %post of a kickstart.

I am wondering why this import is not happening automatically at install time. There must be good reasons for that?
-- 
Markus