Why is the yum exit status on "Nothing to do" returns different in between Red Hat Enterprise Linux 5 and 6?

Issue

• When running a yum command where the result returns that no actions are necessary, the exit status of the yum command is different between Red Hat Enterprise Linux 5 and 6:

[root@system ~]# cat /etc/redhat-release 
Red Hat Enterprise Linux Server release 5.9 (Tikanga)
[root@tester ~]# yum install tester
Loaded plugins: rhnplugin, security
This system is receiving updates from RHN Classic or RHN Satellite.
Setting up Install Process
No package tester available.
Nothing to do
[root@system ~]# echo $?
0


On RHEL6, yum exits with a status 1:
[root@system ~]# cat /etc/redhat-release 
Red Hat Enterprise Linux Server release 6.3 (Santiago)
[root@system ~]# yum install ipvsadm
Loaded plugins: product-id, rhnplugin, security, subscription-manager
Updating certificate-based repositories.
Unable to read consumer identity
Setting up Install Process
No package ipvsadm available.
Error: Nothing to do
[root@system ~]# echo $?
1