Simply put, Web sites probably support two functions: one as a content provider, and the other as a channel that allows your users to interact with you or each other.

Arguably the first describes the original Web; a collection of sites that publish content for users to consume.

The second type is probably most concerned with taking 'bricks and mortar' business to the Web.  This could be for a number of reasons including reaching a new market that the original business could not.

Of course most sites support both types of functionality.  But is this difference taken into account when creating the user experience for the site?