GNS and Big Model theories have limits. They describe the players, the relationships between player stances, and the social contract between the players. They help expose the incoherences and/or game design flaws of role-playing games. They help understand the psychological mechanics & dynamics of a RPG gaming table. They help understand that differing expectations will end up with incoherence, zilch play, or even agenda clash. In that, they are useful awareness-raising tools for the GM and the players alike.
However, they also show their limits in that they are theoretical tools, from which GM & player best practices have to be deducted, and depend on the effort of the GM, on his understanding, and on the willingness and/or ability of each player to understand her own creative agenda, her own needs and expectations, know her own stance and the nature of the game, and fulfill her part of the gaming table "social contract".
But what of the time-deprived gamemaster? What of the player who is unwilling or unable to clearly state or even understand his own expectations?
Moreover, what of the case of an impromptu gaming table, or a gaming convention demo? How can a GM apply his understanding of the Big Model or the GNS model to the gaming session at hand without engaging in interviews on the preferred creative agendas and expectations of the players?
I believe that these limits can be broken through by any GM, by adopting a common, game-independant, player-independant, creative-agenda-independant methodical gamemastering approach.