I know what you mean. We have the guideline there, but we don't enforce it. But that's not an oversight on our part.
If new members picked the right section for their posts, it would cut down on the work for staff members and the new members would get answers faster. Like Frisco said, we have the guideline to encourage that behaviour.
But people ignore the guideline all the time. And really, we have no way of preventing that. They are new members to the forum, so that thread is our first point of contact; there's no opportunity to tell them otherwise until the damage is done and they've already posted in the wrong section. Nearly everybody gets into the swing of things within a few posts, but there will always be new members arriving and making the same mistake.
Removing the introduction section won't stop them either. In the past we've tried rearranging the front page, and these support threads tend to accumulate in the first section on the homepage, whether it's the introductions section or not. That taught us that these posts are just something we have to deal with.
In the end, having the introduction section means that we can allow these posts to accumulate in one section without disrupting the other, more useful sections.