x2. Just ask the mods what it costs to run and maintain a web site. I am on Stalkbook and often see all sorts of companies on there and get frustrated that they don't have a proper web site I can get some decent info from. However in this day and age when everyone is out to find as many cost cutting measures as possible, online presence costs can be reduced by advertising on social media. Frustrating, but a sign of the times IMO.
forums etc are far different to a static website. however, a forum isn't really that hard if you have moderators editing content etc
a simple website with info, basic blog, and images is a piece of cake to setup, and costs hardly anything.
anyone can make up their own for minimal $$.
you can setup a website in a few hours for free, or buy a template for $90! annual hosting charges are as little as $100.
I have built a few websites, and whilst the better ones (flashy ones) take much time and effort - the sort of businesses using facebook only wouldn't have a need for a serious website with many features.
i don't think they are cost cutting - I think they think that everyone is on stalkbook, and therefore its the best and easiest method to reach as many people as possible.
personally, i recommend at least both channels. I am not on stalkbook either, but where a business chooses to use it only and doesn't have a website, i shy away from trusting them as it somehow feels as though they aren't a solid or trustworthy business - just a personal feeling i get about it.