I think you guys are vastly overcomplicating the realms notion. I think the simple, yet effective answer is to take a page out of 40K: you have the material plane that obeys physics and the immaterial plane which does not obey physics, is the source of all supernatural power, is home to its own host of (presumably dangerous) supernatural creatures, and is used as a bridge to cross immense distances in the material plane easily (distances not feasibly traversed through any available means).