Good social media tools let you get your message to everyone who has internet access, but do you need to reach the whole world?Twitter has millions of users around the World. Do you sell your service around the World?
W3C has a new accessibility section. It does a nice job of unifying their accessibility content into one location. The home page has a great explanation of the three W's of accessibility. Why, What, and How. (Two W's and an H just doesn't have a nice ring to it.)