Two Centos Machines. Wildly different updates
CentOS 5.4 was just released. I believe it's still making its way through the mirrors so check to see if the machines are using the same mirrors for their updates.
On developer machine repository centosplus is probably enabled.
Try running:
yum clean all
To remove the cached headers, etc. Then try the update or check-update again.
What is the output of cat /etc/issue on both systems?