Drew said:
In other words, is it an earth-sized sphere orbiting a sol-like star? Generally speaking, do the rules of physics of the real world apply to your fantasy world?
If so, why?
Yes, because it's just easier that way. In more detail:
1) Changing the fundamentals requires that players learn and remember those changes. Fundamentals include a moon and tides, a 24 hour day, a 7 day week, months that are roughly 28-31 days long, how falling things behave, etc. In my experience, unless all of the players enjoy learning exotic details of fantasy settings, many players are going to treat this as a chore rather than a pleasure.
2) I like games that focus on characters and events rather than scenery unless the scenery is special so I want the mundane parts of my setting to be background, not foreground. Put yet another way, when all of the scenery is special, none of it is.
3) The implications of changing how the real world works are not always obvious and having an unexpected implication became a major factor during play can be disasterous to versimilitude. And where they are obvious, the setting usually jumps through hoops to emulate useful elements of the real world (e.g., tides, days, varied weather) when all of those useful elements come as part of the package with a realistic planet.
Drew said:
How do you feel about flat worlds? Worlds where the sky is actually a demi-plane hung with crystaline lanterns. Worlds where sailing east will eventually result in falling off the world. Worlds where the sun is actually a burning ship drawn across the sky each day by magic flying condors.
What's the purpose of making the sun a burning ship being drawn across the sky each day by magic flying condors? If I want the sun to move across the sky to create day and night, I can get that with a realistic planet. If you are going to go through the trouble of creating an exotic cosmology, it should behave in exotic ways and rather than simply emulate the behavior of a planet. For example, on Larry Niven's Ringworld, one can see the arch of the ring, the horizon actually curves up into view, it's always noon because day and night are created by shades that block the sun, etc. The movement of the Sun explained as a burning chariot crossing the sky only happened because people couldn't think of a better explanation for the sun or it's behavior.
Drew said:
Are there worlds out there that actually reflect medieval "science" and superstition? Do you think it would be cool to game in such a setting, or would it strike you as "wrong?"
I don't consider it wrong and there is certainly a segment of role-players who enjoy such games. Personally? I think its often just tedious fluff that doesn't really add anything to the game. So what I'd say is that if you are going to go through the trouble to create an exotic world or cosmology, it should serve some interesting purpose in the game and not simply be annoying complexity just to be exotic and different.
Drew said:
Why do we have such a proliferation of "mundane" worlds in a magical/fantastic gaming genre?
One of S. John Ross's five elements of a commercially successful role-playing setting -- cliche. When a game includes familiar elements, they become background elements that the players are familiar with and comfortable with using. When a game includes unfamiliar and exotic elements, the players have to consider everything that they do and can take nothing for granted unless they spend a lot of time studying the setting. As I mentioned earlier, a lot of players consider that a chore. They want to do more with their character than learn the mundane details of life necessary for basic communication and survival. Yes, there are plenty of players who enjoy exotic settings and details but also plenty who don't.