Being found online is important, but being found on the right search engines is even more important. There are a lot of search engines out there, most of which are only used under specialized circumstances. It doesn’t matter if your site is easily found on any of them unless they actually pertain to what you do.
The only ones that matter are those that are intended for what your website covers and major engines like Yahoo! and Google. So long as you’re easy to find on them, you’re fine. Otherwise, your site is in real trouble, because the only people who will be going to it are those who already know about it – that means little or no new business will be coming your way.
That’s where SEO comes in, actually. It makes sure that your website works with the search engines that you need to be visible on. That way, the only limit to how much business you see depends on your own efforts to satisfy your clients. Since that’s the way it should be, you need to be absolutely sure of what search engines you need besides Google, if any.