The reason social networks are not for pay is because of "network effects":
http://en.wikipedia.org/wiki/Network_effect
It's hard enough to get a network going, let alone make people pay for it.
http://en.wikipedia.org/wiki/Network_effect
It's hard enough to get a network going, let alone make people pay for it.
It sounds cyclic. Social networks need lots of users because they can't charge their users directly, and they can't charge their users directly because they need so many users.
I don't know that app.net has to replace Twitter for everyone. Can't they be smaller and yet successful, precisely because they charge users directly?
Therefor, to offer the most value to users, those building social networks want to get rid of barriers (including payment) that might prevent more people from signing up. That, then, gets reinforced by the cyclic relationship between the fact that indirectly monetizing users tends to pull in relatively little per user while marginal costs of hosting an additional user are minimal - but the initial dynamic is an artifact of the nature of social sites to begin with.
Before facebook, social networks could provide a lot of value by saturating small demographics. Example: If all Swedish teenagers are on playahead.se and can all talk to each other there, they don't gain much from network expansion. The reason those networks need to grow beyond the clique where they're successful is that their business model can't sustain itself on a small number of paying users.
If app.net saturates the demographic of "people who care enough about Twitter's new API to chance $50 away," I could talk to 50% of my Twitter circle even if the total number of users on app.net is only 1% of Twitter's.
join.app.net is making the same mistake as diaspora, facebook, myspace, etc. You can't charge someone real money when you aren't the one providing the value.