In OS X 10.6.x you will have iChat 5.x.x and the version numbers of each that you have posted are a match at that level.
However it will not be iChat 5 that is used in OS X 10.5.8 (that will iChat 4.0.8 which is sometimes displayed as ver 4.0.9 depending on the order of a Security Update).
Have you set up Parental Controls on one of these computers ?
If you have then iChat can have all Buddy List Blocked (you then allow Buddies to be seen in the Buddy lists)
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