This has been said many times, and in many ways, but Dave Winer has put it very clearly, and in a way traditional publishing organisations should take to heart:

A long time ago I discovered this fundamental rule of the net — People come back to places that send them away. Places like Google, Yahoo, Craigslist, Youtube, even Twitter. These are the mainstays. You go there to get somewhere else. Sites that try to suck you in and hold you there, no matter how cleverly, go away. While it may seem like a good approach at first, long-term it’s a losing strategy.