Well I think each type of clan helps their own sub-community well, lets the people within that community have some type of "official" connection other than being interested in the same thing. So like artist clans will be able to bounce ideas off each other and such.
Honestly the "Toribash community" really encompasses so much, there are so many ways people use this game and forums. Some people never use the forums, some people never play the game, other people never play singleplayer or never play multiplayer. Helping the entire community is almost impossible, so by making a niche clan you're helping the part of the community you're actually interested. I don't know how you can have a clan that encompasses a large variety of aspects of the game where all the members talk to each other and stick together.
Also I'm just going to assume replaymaking clans are included in artist clans ;o