To keep the feel of it being actually something from DnD intact, I do agree it'd have to have an "Earth people in a different world" set-up. It may be harder to do right, but that doesn't mean it's impossible. (For instance, if it's set up like people actually playing the game and switching between worlds and showing real-world stuff as well, that'd give you a whole extra dimension. One player could be in it to cope with his depression, another to make friends and not actually be interested in the game at first, there could be the divide between the roleplayer and the powergamer, who later come to see they're not so different after all, for you Stormwind Fallacy lovers out there.)
Furthermore, that might actually make it more interesting to people who don't play DnD, as you have to take into account the people who aren't the direct target demographic. It's also much more likely to be watched by kids, so throwing in certain things like language barriers is a bad idea (at least right from the start, I do think that the main characters running into it later would be a nifty idea and embroil them into the setting further). Making the characters come from locations in the world that the people most likely to be watching them is also the most logical, but this doesn't mean they couldn't have connections to other parts of the world. For instance, if you have an Asian in the group, perhaps he only moved recently from Malaysia and got into the group to make friends, not knowing anything about the game. Such a thing would be easiest if the characters either work at an international company or all go to some university with a high level of foreign students.
Originally Posted by Aotrs Commander
Edit: In fact, it occurs that the other advantage is, if you set it up right, the Earth people would not need to have the desire to return home to their families (the Romans come from Pompeii - perhaps the eruption was caused BY the BBEG in his attempt to conquer a new world, or from the fall of the First Empire in Egypt or something), and the story can be about something other than their attempts to get home. Which a) has already been done, b) runs the risk of giving you either an Endless Quest (dull) or a strict cap on the length when the goal is achieved (with potential dubious undoing of the end when it's decided to do One More Season/the Movie.) It'd give you a more open-ended myth arc, because it wouldn't have to end with "beat BBEG."
If going with the "Earth people in a strange world" approach without them actually playing the game or such, this could also easily be done in the modern day. Maybe one of the characters lost her father to gun violence after her mother left or something and doesn't want to return to a world where she is alone. Stuff like that.