Okay thank's for the links people I've so far read the Wiki link on GNS theory and the "System Does Matter" essay.
Considering I personally have played in or run campaigns (not just tournaments) for
AD&D, D&D, D&D 3+, Cyberpunk, Everway, Conspiracy X, All Flesh Must Be Eaten, 2300AD, Traveller: The New Era, Shadowrun, Vampire, V:DA, Star Wars D6/D20, Feng Shui, Champions, Flashing Blades, Dark Conspiracy, Call of Cthulhu (BRP/D20), Cybergeneration, Star Trek. (from memory, so I've probably missed some out).
And enjoyed each and everyone, I fail to see his initial assertion
"Three player aims or outlooks have been suggested, in that a given player approaches a role-playing situation pretty much from one of them, with some, but not much, crossover possible."
Admittedly a lot of those games fall into the Gamist or Simulationist, group but then that's what most major RPG Publishing groups print, the Narrative games I have played/run I've enjoyed as I have enjoyed the Narrative aspects of other games.
Saying there is little or no crossover possible, just isn't my experience, I've been in several groups that have run a wide mix of games with several players taking turns at being GM. So I'm not the only player or GM I've come across that enjoys a variety of playing styles.
Also surely if you have an RPG that is say 50% Gamist, 30% Narrative and 20% Simulationist at least people that have a preferance to the Narrative style are supported to some degree. Not that any game has fixed percentages like that, after all a narrative player will make better use of the narrative aspects of the game, so will get more than say 30% out of it.
If a game just was 100% Narrative or 100% Gamist then I wouldn't be able to play with my friend who happens to prefer the Simulationist style if I prefered the Gamist one.
With that in mind most of the rest of his essay falls to pieces.
Sure you could have a game with 100% Narrative style, and the Narrative GM would then not need to do any work adapting the system to his prefered way of playing, but then he'ld have to find Narrative players to play with. If could well be his best mate is a bit of a Gamist, and the only Narrative players he can find are real jerks (stealing all the Cheetos!).
Surely is makes sense to design a RPG for a broad market, then GM's and players can take what they want out of it, a bit of G with their N and S.
Not only will it make it easier to find someone to buy your product as it will have appeal to G, N or S GM's (and even GN&S GM's like me) but it will make it easier for those GM's to find players, as they can appeal to G, N or S players (or GN&S players like me).
Edit: Having looked at RPGPundit's Landmark's post my ideas seem to fit well with Landmark 4.