Wellm the point was not so much the subpages as the magic "/", which would make a backlink to "GNU" on the "GNU/Linux" article and the like.
It does, in the current implementation (however, if "GNU" does not exist, it does not add a backlink). This was necessary to "grandfather" existing subpages, as Zoe put it. The alternative would be to use another magic character which is currently not allowed in titles, to add an is_subpage flag, or to use a more complex logic that does not store the parent page in the title.
Regards,
Erik