I don't think so. Open source is supposed to be free for everyone, free to modify but not sell as say when you'd sell stuff made after J. R. R. Tolkien's works.
They are freely distributable since editors could just reupload the modified versions. Otherwise, there won't be any point of open source rather maps would just be unprotected which many already are.
Are you confusing public domain with open-source?
I'm pretty sure open-source is a historic concept so it already has a meaning. In this context open-source is a licensing standart (non restrictive modifying, distribution, and overall use of the code) regarding software CODE. If you say a piece of code is open-source a great deal of people will automatically assume a certain meaning and reasonably so.
Most programmers are familiar with this open-source concept as well as the free software movement, but also most programmers think that the only possible copyright implicated on a
game is the code. On a game you have assets that are the creation of, most likely, a 3D artist or a composer. Already lots of courts recognize that games themselves are another possible separated IP (the author here is the "game developer", just like on a movie there is a script and art, but there is also
a director). A court ie. recognized that DotA (Wc3) implicated IP as a game ("audiovisual work"), even if the authors used assets of Blizzard. This means that the game is a separated IP from the assets and also the code, as the code is considered a "literary work".
A game that is solo developed is certanly possible (the ownership problem becomes simplified here), but on a custom wc3 map you will see code and assets made by lots of different authors (including ie. Blizzard). I noted this problem in one of posts above: the HIVE open-source definition implicates a license over the code? the assets? the game itself? all the above?
So let's apply all this: the HIVE here says that an entire game project is
open-source. Again, a great deal of people will assume a certain meaning already: free modification, free distribution and overall non-restrictive use of the
game. Luckily, and as i said, the "HIVE own Open-source Definition" is clear in saying that open-source only means free modification. Still, because of the use of a concept that already has a meaning for a great deal of people, i'm certain that we will get into some discussions regarding on what rules apply, yet again.