I see. Obviously you know much more than I do regarding this subject So I'm asking another question, maybe you have an answer for this too: what's the status of this Empathy project? Does it still get updated or is the project dead? For some reason, I prefer it to Pidgin, the Adium themes work just fine with it and if those bugs that I was talking about are removed, it could be the best I've seen for Linux.
Empathy was created a few years after I stopped being involved IM-development (I got an education instead ;-)). Seems to me it is still actively developed (it is distributed with gnome after all), but I would doubt new features, etc. are focus for the YIM portion. It does have XMPP video call support. That's what all the clients evidently have, I suppose since it is an open protocol.
To be perfectly fair, iirc, yahoo created multiple versions of the yim protocol, and it is more than likely that the majority of 3rd party clients are using an older version of the protocol which doesn't support video. Speaking of Adium, last I recall it uses libpurple from Pidgin so I imagine it also has the same limitations that Pidgin has (but for OSX). Though, I'm sure many people consider it to be prettier.
EDIT: looks like the file-transfer thing in empathy has been a known issue with yim for years.