Some new members just don't bother with the first and easiest step of joining a new forum. It doesn't hurt anyone if they don't introduce themselves.
Though it is the best way to get to know members of the forum much easier, and a good place for a new member tpo ask questions.
Some members are just ready to dive into the content of the forum. I get alot of new members, who skip the introduction process and go straight to the boards for brawling.
It doesn't really bother me... You can't force a member to introduce themselves (well you can but it isn't a good start for the member if you come down on them hard first off and make them post an intro).