I would generally agree with/support this as well.
I'm curious as to how you're able to see Spartan's new avatar in older posts, as at last check older posts did not use the current avatar, but the avatar that the person had at the time (very confusing and I have no idea why, especially as this means it must already save multiple avatars in the system, most of which are not even wanted to be used any longer), but to be honest I haven't looked into this in more than a week so I suppose that it is possible that it has changed.
Short version: Older posts should show current avatar if they do not already. If they do, could someone link me to the update to the forums that specifies this, if there is one? It was not working like this for me as recently as two to three weeks ago.
On a completely different tangent, I'm curious as to why the karma is separated on a site-by-site basis. I would say I'm probably fairly well known on the GCII forums (I think I may have the highest karma of anyone without an avatar, haha), but when I went over to sins with a problem, no one knew me, and in fact the only people who responded were people I'd already seen on the GCII forums. This may also have had something to do with the fact that it was a problem most could not contemplate existing, let alone fixing, but I'm beginning to see the same thing here now as well.
Short version: I personally think the system might be improved if the karma was on a global basis. As the forums are all essentially one and all threads do actually exist on all sites (that I am aware of), this should not be terribly difficult, except for perhaps setting a [forumname] parameter before the [post number] in the link, which, no offense, but I can do that with my eyes shut.
EDIT: Apparently karma actually shows up in a user's profile regardless of site, but is counted on a site-by-site basis. Isn't that silly?