The Web is about communication. The Web gives a chance for new kinds of roles to exist among people who provide and consume information, communicate, and interact. The Web is a unique kind of medium for communication and is another step in centuries of change in the way people use media.
The Web isn't just technology, although its operation depends on it--the Web does have a technical basis as a client/server system for hypermedia communication. But not all the jazzy-interactive software in the world will convince you or anyone to use the Web and abide its curious unpredictableness and chaos--there's probably not a single compelling reason to use the Web, but rather a collective set of personal opportunities that each person decides are important.