It's not network effects. It's hostile copyright and network access law. There's no reason that you shouldn't be able to interact with the content streams from

It's not network effects. It's hostile copyright and network access law. There's no reason that you shouldn't be able to interact with the content streams from both Twitter and App.Net at the same time, for example, except that our legal system allows the dominant company to sue the scrappy upstart into oblivion if they begin to do so. This is not theoretical; small companies are destroyed frequently by BigCo breaking out the lawyers for supposed violations of the CFAA and the Copyright Act. This sorry legal situation has completely obliterated meaningful competition in the online space, and we are letting them get away with it when we just hand-wave that it's because of "network effects". There's no reason that YoungSiteA shouldn't be able to act as a user agent on my behalf to access and reskin OldSiteB. If it could, the negative impact of switching providers would be small.