In context it means all user content submitted in the games is effectively fully owned by Blizzard, a copyright assignment clause (this differs from the typical “we get a perpetual license to what you submit to us”)
I understand what you mean now by them saying you wave your moral rights as a matter of giving up your rights to any product you create.
Still seems immoral of them to just grab your creations and claim it as their own, but "viva capitalism!" I guess.