firstly, the timeline is in the late 1930s, so the technology is closer to WWII than WWI.
also, it's a lot more "pulpy" and more "cinematic" than a typical air combat game. look at some of the plane designs -- a lot of them aren't even aerodynamically stable (they wouldn't be able to fly in real life, or so i gather).
the game's more about "thrilling adventure!" and "aerial derring-do!" and not just a game of some planes shooting at each other.
also, the backstory (while a little far-fetched) is kinda neat -- a balkanized America. with some of the new American nations favoring Britain, or France, or the Soviets, or Germany -- and it's 1938 in the timeline... well, things could get interesting in North America very soon...