I think everything talked about here is sci-fi, but which sub-genre seems to be the debate. I'm especially puzzled by Fury Road as there really is no technology or fantasy element to it. It's the post apocalypse and people are using primitive means to fight for precious resources.
Is that enough to be sci-fi? Are stories like The Road or Book of Eli also Sci-Fi because they are post apocalypse? I can see zombie apocalypse being sci-fi because, well zombies are science based and/or fantasy. What are the base requirements for sci-fi?
Setting it in the future is a sufficient, but not necessary, component of science fiction. The post-apocalyptic tale is a staple of science fiction, and a popular sub-genre.
While I am not a huge fan of Orson Scott Card, I do think that his overall scheme is fairly good for science fiction in delineating the five types of tales that people generally consider science fiction:
1. All stories set in the future, because the future can't be known. This includes all stories speculating about future technologies, which is, for some people, the only thing that science fiction is good for. Ironically, many stories written in the 1940s and 1950s that were set in what was then the future—the 1960s, 1970s and 1980s—are no longer "futuristic." Yet they aren't "false," either, because few science fiction writers pretend to be writing what will happen. Rather, they write what might happen. So those out-of-date futures, like that depicted in the novel 1984, simply shift from the "future" category to number 2 ...
2. All stories set in the historical past that contradict known facts of history. Within the field of science fiction, these are called "alternate world" stories. For instance, what if the Cuban Missile Crisis had led to nuclear war? What if Hitler had died in 1939? In the real world, of course, these events did not happen—so stories that take place in such false pasts are the purview of science fiction and fantasy.
3. All stories set in other worlds, because we've never gone there. Whether "future humans" take part in the story or not, if it isn't Earth, it belongs to this genre.
4. All stories supposedly set on Earth, but before recorded history and contradicting the known archaeological record—stories about visits from ancient aliens, or ancient civilizations that left no trace, or "lost kingdoms" surviving into modern times.
5. All stories that contradict some known or supposed law of nature. Obviously, fantasy that uses magic falls into this category, but so does much science fiction: time travel stories, for instance, or "invisible man" stories.
What makes this taxonomy useful is that, generally, the five categories also (IMO) also happen to correlate, generally, to how most people view the science fiction categories. 1 is always a no-brainer ... while 5 is often contentious (fantasy or science fiction ....).
Most importantly, it shows how broad the overall category is; it's like saying "Rock and Roll" music and then getting into a debate about how this year's finalists for the Rock and Roll Hall of Fame include Judas Priest, Eminem, Kate Bush, Dolly Parton, Fela Kutti, Rage Against the Machine, Lionel Ritchie, A Tribe Called Quest and Dionee Warwick.
