The iChat 2.1 update is to update version 2 (which was a very long time ago)
It is the only update you will find by searching.
Other than two standalone updates during the the effective life of iChat 3 all other updates have been included as part of the OS X updates (when iChat has been updated)
That is to say, when there is an iChat Update it is in the OS X update although not all OS X updates have iChat updates in them.
Mountain Lion has Messages.
This is a new name for the App which also has a major new feature is being able to send iMessages to iOS devices via Apple's new iMessage service.
Under the hood Messages is like having an iChat+
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Mountain Lion 10.8.2)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad
"Limit the Logs to the Bits above Binary Images." No, Seriously