The whole point of fire/water/grass is that the other types would either be not or super effective against each other. the only other type combo that works well is rock/flying/fighting --- Black Nuzlocke: [see link and team in quote] Official Grand Master Flygon of the B/W boards and Face-Ripping Club...
They don't just do that for tradition. As we all know, Pokémon is also a children's game. It does have an in-depth side, the metagame, competitive battle and stuff, but primarly it's aimed at kids. And not all kids are familiarized with weaknesses and resistances, so they have to start with an easy triangle. Grass, fire and water is easy to remember. Their weaknesses and resistances are obvious. They are good for beginners. Whereas other type combos aren't.
The 3 ones mentioned in this topic:
ground/rock/steel -> First of all, it's not even balanced. Ground is supper effective against both, and none is supper effective against it. Besides that, it's not obvious for everybody that steel is supper effective against rock or ground is supper effective against steel. Beginners would be confused.
dark/psychic/fighting -> Extremely arguable triangle. Discussions about this one have been happening since gen 2, probably. Beginners aren't supposed to be dealing with immunities so early in the game.
flying/rock/fighting -> Again not easy to figure out. Imagine little kids trying to figure this out. I for one wouldn't guess flying is strong against fighting.
Basically, that's why they stick to the GFW triangle. The weaknesses and resistances are easy to figure out, kid-friendly, and have worked since gen 1. --- Hey everybody, I'm back from the dead! =D SoulSilver FC: 3825 1407 2219
Fighting/Dark/Psychic works wonders.Tho Ghost would be more sensible instead of fighting. --- Currently Playing:Pokemon Heartgold,Fallout:New Vegas,GOW:GOS,Naruto Storm 2,COD:Black Ops,Blackshot,Grand Turismo 5.Waiting for:Pokemon Black English,Disgaea 4
Fighting/Dark/Psychic works wonders.Tho Ghost would be more sensible instead of fighting
As I said, it's argueable, because of the imunity. It works? Yes and No. Ghost instead of fighting would make it unbalanced. Dark and Ghost would be strong against Psychic, and Psychic wouldn't be strong against anything. --- Hey everybody, I'm back from the dead! =D SoulSilver FC: 3825 1407 2219