In some RPGs players think of a story and then find rules that fit the scenario. A great example are rules for an ambush or surprise. If the game master (GM) feels the story calls for using those rules then they will be put into effect. The story inspires the game play. Moving from story to rules can work if the GM is fair and the players are well-mannered. But even still the story can often run into situations where the rules don’t quite fit. Great GM’s can roll with it, making game design choices on the fly. Less experienced groups will often simply experience poor game play.
Seed rpg Flows in reverse. The system has clear game play oriented choices. These choices are then explained with a story. The game play inspires a story. In theory this would appear to limit the potential of your storytelling, in practice the challenge of explaining game play results as a story is both fun and interesting.
The flow of rules into story means the rules will never break at the hands of the story. A compelling game is ensured, with the right gameplay, fiction and imagery coming up with a story to fit is easy. You’re at the table to tell a story right? When you don’t have to worry about the rules breaking storytelling takes center stage.
This flow is very common in new rpgs, if your interested in alternative role-playing games check out http://www.story-games.com/forums/ and ask for some recommendations!