xchat-gnome started as an interface for xchat that was meant to follow the Human Interface Guidelines. To do this, many of the preferences were removed from XChat's interface, instead relying on overall GNOME settings. The end result was that the interface became radically different from XChat's.
Ubuntu has marked xchat-gnome as a primary package, and so many users will inadvertently install xchat-gnome instead of XChat. The interface is quite limited, and the similarity in names causes some people to believe that xchat-gnome is handled by XChat developers. This is not the case, as xchat-gnome is now a complete fork.
If you are running Ubuntu and currently running xchat-gnome and would like to run XChat instead, see Yvonne's guide to switching from xchat-gnome.