[CentOS] Why does CentOS 3.X still use yum 2.0.8?

I understand that the CentOS packages track the upstream vendor's 
packages as closely as possible.  In the case of yum, which as far as 
I'm aware is added by the CentOS team, I'm curious why it isn't upgraded 
to a newer version that uses the repomd format.  "yum" operations on 
CentOS 4 seem to be significantly faster than those on CentOS 3.  I 
recall a yum upgrade happening between CentOS 4.1 and 4.2, and I'm 
wondering if such an upgrade could happen on CentOS 3 as well...

Thanks,
Greg