Zileas: A good world design provides a meaningful context for the game, and in that respect it's immediately useful to the game in a pure multiplayer scenario. If the units are just random things that have abilities and very little character, the game just isn't as immersive.
As you mention, we have no single player in this release (though we may release a single-player version which would build on this). It's important that we go out of our way to set the framework for a world, otherwise I think you will lose a lot of important ambience that fills out the gameplay and gives it a sense of completeness, even if it really has no actual meaningful effect on the game.
Thirdly, and this no doubt ties in with other things we'll talk about, we are trying very hard to make our game easily TC-able (totally convertable) and also want to encourage other fan activity such as maps, fan fiction, etc. If you don't have a world to go with the game, that sort of activity won't get inspired as much. I think that having a strong community of people modifying/adding to the game after it's out will greatly increase the replay value of Strifeshadow.