During the BETA of vSphere 4.1, there were some inconsistencies in some of the build numbers which was eventually resolved. It looks like something was still missed in the final RTM release of vSphere 4.1 ....
Here is a screenshot of the python libraries on classic ESX 4.1 used for esxupdate. At some point, it looks like this release was going to be named vSphere 4.5 as most people had anticipated, but then was revised to 4.1.
I'm sure there will be few more easter eggs, happy hunting 🙂
Thanks for the comment!