Social media page vs. traditional website

Some (consumer goods) companies have tremendous success driving traffic to their social media pages. Coca Cola for example has over 30 million visitors per months on its Facebook page. Many of these visitors like the site and interact with it. Starbucks and some other consumer brands have similar success on their Facebook pages. In contrast, the activity on these sites' classic homepages is relatively low (in the case of Coke it is around a million visitors a months). Should brands move their representation entirely on social networks (Facebook essentially or maybe LinkedIn for B2B brands)? This would be quite a change for marketing practice. Yet, increasingly this makes sense.