[CentOS] After 5.1 update $releasever is still 5

Tue Dec 11 13:47:50 UTC 2007
Robert Moskowitz <rgm at htt-consult.com>

I have performed the 5.1 update via the 5 repo on a couple of systems.  
I then went to switch these systems to my new local repo using ther 
$releasever variable.  It still has the value of 5, not 5.1

Where is this set?  Why was it not changed to 5.1?

On the one clean install from the 5.1 isos, $releasever is at 5.1   I think.