Not at all. As a design for a game that develops coherent story, narrower focus is so very much better. I think GoB (before I took it over, and continuingly) did have some elements of being an answer to other GoT games being draconically narrow in their list of playable concepts, so it's rather wide open.
Though the practical (rather than "this is just the way we chose to do it") issue I'd see with focus on a single family is how incompatible that can be with player turnover. I see that as a major flaw of GoT as a MUSH setting in general -- bugger playing pre-made roster characters, I think most people want to make an original character. But in spite of the source material's habit of having people die practically at random, characters wandering off the game because of players having other shit to do leaves PC families in weird places. Also that thing where some people really hate it when they just suddenly have a brother who was never mentioned before.
