That's a good way of looking at it, and it's what I typically do. I just felt like theorizing a bit. :)

---SRSBZNS---
The main issue I have with the "alternate reality" explanation is that in some cases, the fiction has had a huge cultural impact. Particularly in near-future speculative fiction, the world they talk about might not exist if the genre, or even the specific story, hadn't come to be. An example would be modern-day superhero movies about characters whose previous adventures have shaped generations - but those comics and older movies don't exist in the movie, so the world really shouldn't look the same.

This is a thing I feel Hellboy dealt with quite well: in one of the movies (I forget which), Hellboy actually has a few of the previous Hellboy comics, so it meshes in quite well, with the original comics being inspired by "Hellboy sightings".
---/SRSBZNS---

Halo, of course, isn't hugely affected by this as it isn't near-future or modern-day, but I thought it would be interesting to speculate on the subject. So I did!