What I believe is at the heart of our veneration and fascination with the apocalypse is the concept of the sublime, or in its modern iteration, the uncanny. The sublime, in its 19th century guise as described by for instance Burke, can essentially be defined as an expression of the most basic of human emotions: fear of death. Any sublime thing, be it a spewing volcanoe or a towering mountain, a ship lost beneath the waves or a field of battle, will resonate with our deepest instincts of self preservation. That is why we gravitate, helplessly, towards scenes of ultimate horror, such as the apocalypse and the post-apocalypse, simply because it summons such emotions in us. Burke added a moral element to the sublime: by subjecting ourselves to it (be it in reality, or in a painting or through some other work of art), we steeled ourselves in a way that was not possible when merely subjected to the beautiful - the antipode of the sublime.
In more modern days, the psychoanalytical concept of the unheimlich, the uncanny, might be a more fitting descriptor of why we are so fascinated with the POST-apocalypse. In the post-apocalypse, all the things we took for granted (society, law and order, but also space itself - cities, countryside, roads) will have been irrevocably changed into something which is nearly-familiar yet at the same time completely different, and therefore uncannily terrifying. Ruined cities, ruined people, a civilization in tatters - what's not to be fascinated with?
In a wider sense, as some of the articles have postulated, the 'apocalypse' can be given such a wide definition that it fits in almost any narrative (maybe Proust is post-apocalyptic, for instance - 'À la recherche du temps perdu' is ripe for a post-apocalyptic re-rendering à la 'Pride and Prejudice and Zombies'). But even in its narrower definition it's a trope used almost universally, especially in an interactive medium such as a game - it doesn't take much to evoke a post-apocalyptic wasteland, with the uncanny and the nostalgic mingling freely to create that indelible, sublime exhilaration that comes from knowing this might be your future too.
Oh, and good post!