The last one is just because 40K came out of another game "Warhammer Fantasy Battle" so the marketing originally stated that "it's like this other thing, but in space". That wasn't needed once it became it's own established brand.
Didn't that piss off the fandom? I mean, telling the fans one origin story only to retcon it and say "nope, it is something else" is kinda unfair. Also, isn't that a bit risky for the business?
Also, thanks for answering LordBaal and Trekkin.
Lord, I know I ask too much now, but what is the deal with this Matt Ward and C.S? I know from 4chan wiki that Matt used to "fanboy" the Ultramarines. But I don't really know much else.
Also, yeah Necrons! Or how 4chan refers to them as "space egyptians". Although, why are they so feared by every other faction? I know that they are super strong and that "they come out of the damn walls", but like with Ward, I don't know else.
It being Fantasy in Space was marketing, not an origin story.
Basically 40k was based loosely off of Warhammer Fantasy with some factions being loosely based on the Fantasy version. Squats were steampunk biker versions of Dwarves, Eldar were Elves, the Imperium was based off the (Holy Roman empire inspired) Empire with some sci-fi dystopia elements added, the Orks were Orcs. At the time 40k was a mish mash of pop culture references, bad jokes, historical nerd jokes and 80s subculture references. When they sat down to make 2nd edition and make the setting more formal they scrapped a lot of it and redrafted it, mostly making things more cohesive and dropping a lot of stuff they couldn't be bothered with like Squats and the shark people aliens. From 2nd edition onwards the setting has largely stayed the same beyond adding new factions and the odd retcon.
C.S. Goto is considered one of the worst 40k novel writers to have ever touched the setting. His books outright contradicted established conventions and rules of the setting, like marines using bolter weapons and Khorne hating psykers.
Matt Ward's main problem is writing fluff in a very fanboyish way, any codex he writes goes more heavy on 'these guys are the bestest ever!' than other codexes do, and his rules writing tends to be overly strong which draws attention to the codex as people jump on the bandwagon.
Necrons are considered scary because they're highly advanced and the main factions have few responses to them. They don't die easily, often teleport around, don't generally negotiate and are usually something you find by accident. They're basically a faceless horror.
Or were anyway. Current Necrons are less feared, because part of making them customizable and personable was making them more present. They now negotiate, are a bit less individually strong in most portrayals, and are often long enough for them to become known quantities in their area of influence.