[jlam]

I don't know how you could say that. If anything, the article calls for the demise of walled gardens:

“Early services, such as CompuServe, Prodigy or AOL, began as ‘walled gardens’ before they opened up to become websites. The early e-mail services could send messages only within their own walls (rather as Facebook's messaging does today). Instant-messaging, too, started closed, but is gradually opening up. In social networking, this evolution is just beginning.

“‘E-mail…is the most important social network’… because the extended inbox contains invaluable and dynamically updated information about human connections.”

Without pressure to make it a business, e mail “can remain intimate and discreet. Facebook has an economic incentive to publish ever more data about its users…but [traditional e mail] can let users minimise what they share.”

[tim2]

Still just vague analogies. It's not that hard to give a more concrete example of what's possible. Why don't people do this? Because you'd see that this doesn't really provide anything compelling at all.