Marketing via Twitter/Facebook/Myspace

I was searching the recent sites for our class assignment on ranking corporations by their effectiveness to marketing. I was interested to see that Ford Motor Company had a link to find them on the various social networks like twitter and Facebook. I linked myself to the facebook page and found out some information about the company. As most of you already know facebook offers information on events and pictures for the facebook or twitter page. I found that ford had been basically marketing products using the website because from the facebook homepage you could find pictures of recent cars being built and new events that ford was offering for their company. They also link news articles off the facebook sight incase anyone who is interested in different car manufacturing topics can read them. The sight also allows you to share with your friends. Because of the extent to the popularity of facebook, how come not all company's have shifted their marketing towards social networking sights to advertise?