I'm not a big Chris Brogan fan, but his article about Social Media kind of sums it up:
Here’s how I sell social media to companies: “I want to help you get more leads, and/or more sales.” When they say, “How much will it cost?” I say, “less than what you’re paying for mainstream advertising.” When they say, “Which technologies will you use?” I say, “Who cares? Let’s figure out how to help people buy more of what you’re selling.”
Social Media is just a set of tools to get the word out about what you are selling. It's like a print ad, billboard, radio ad, etc. It's new ways to publish your story -- so that others can tell your story or spread the word.