That's the way Favreau wanted it: science/tech-based instead of magic/supernatural. The world of the Iron Man films is our own, except a little more high-tech, that's all. I remember interviews where Favreau was very sceptical of the Avengers, since he didnt think they could put Thor in the same movie as Stark.
Fury tells Stark there are more heroes out there, but at that point it was just Stark, and arguably Widow and Hawkeye. Banner's on the run and not being heroic, Cap's on ice at that point, and so far there is no in-world indication of there being other superheroes active during that time.