I wont argue about names, but the key difference is that Weaver II and weaver II pro were actually two separate themes, and pro being a licensed one it could not be updated via wordpress
With Xtreme things are a lot easier, Everyone uses the same base free Theme which is Weaver Xtreme (along with its free Weaver Xtreme theme support plugin) and updates through wordpress.org.
Advanced users only need to add the “Plus” plugin for added features