What Jeremy said, plus I don't think it's worth carrying an Ubuntu patch for this alone.
The HIG's inconsistency with itself already causes inconsistency in XChat alone: the "Preferences" item doesn't have ellipsis, but all the various "Advanced" preferences items correctly do. So it's not as if Ubuntu is making anything worse.
What Jeremy said, plus I don't think it's worth carrying an Ubuntu patch for this alone.
The HIG's inconsistency with itself already causes inconsistency in XChat alone: the "Preferences" item doesn't have ellipsis, but all the various "Advanced" preferences items correctly do. So it's not as if Ubuntu is making anything worse.