I've seen images of comets arcing through the Myth sky, and a nice even pattern of day/night/day/night, as well as some very nice changing seasons: "Damn I hate the cold". If that isn't evidence enough, I'm not sure what could convince ya.
Although I could agree that the inhabitants of the Myth world may still percieve it as being flat, I find it highly unlikely that the Bungie-folke would intentionally make it so in 'reality'.
Oh, and many of the phenomena that you cite are 'magic' or paranormal in nature, no? so therefore, like teleportation, the Great Devoid would not follow the rules of normal physics, and could in fact be a special case. Using it's existence, or features, to describe the rest of the world would be like finding a cancerous cell and using it to describe a full human body.
Just my 2 cents. *8)
-Santa.. excited as any human could possibly be at recent news.
