New repositories were created a month ago to store old versions of packages that were in the EL5.1 and EL6 repositories, where newer versions are kept. Today, the old versions of these packages have been moved to these new archive repositories.
If you have installed the latest.rpm recently, you will already have configured access to these archive repositories, but otherwise you can get access by repeating installation of the repository version you are using, see the Yum Repository page for details on how to install this.
Archived versions of packages will instead now be accessible for installation via:
yum install package-name.version --enablerepo=webtatic-archive
If you do use the archived packages, please note that using them there may be bugs and security issues that have since been fixed in the latest version of the packages, so if you can avoid it, you should only use the standard repositories.
This separation will mean that the package metadata for the existing EL5.1 and EL6 repositories will be reduced in size now, and mirroring should by default only sync the latest packages. It is standard practice in Yum repositories to delete or archive old versions of packages, Webtatic has taken the latter approach so that if it's critical to you to stay on the old versions, you can still do that.