Facebook and Twitter both can help your business. But it all depends on how you use it. You need to advertise your Facebook or Twitter pages in other areas to let people know you can be found there. Such pages need to be updated regularly.
I've seen lots of different businesses go the Facebook and/or Twitter route mainly because it's very easy to do. The look is consistent and direct. And there's little if any compatibility headaches like you would get from building or updating a separate web site. For instance, lots of new movies from major Hollywood studios no longer have web pages. They just throw up a Facebook page and upload some things to YouTube.
IMHO, "web development" (what they're calling web site design these days) is a mess. Apple got the war against Flash started. While HTML5 is great in concept, its actual support in various web browsers is still incomplete and inconsistent. HTML5 support is worse on mobile devices, smart TVs, game consoles and various set top boxes. Add to this the need to know/learn Java and JQuery programming. With Flash, one could easily put together an animated slide show with little or no ActionScript coding. It takes a lot more time to put together something similar using Java, JQuery, Canvas, etc.
With all of that mess considered, using Facebook seems like a no nonsense idea.