The constant push & pull of open vs closed networks (see a previous post) continues with Twitter as Graham Attwell describes here in the context of education. Building (high) walls doesn’t appear to have harmed Facebook just yet and Twitter’s move should be seen in the context of the criticisms it has faced on monetisation. But then, the same thing was said of AOL (not to mention all the mobile phone companies…. ). But kicking your ecosystem of developers does seem perverse given the “user experience” of twitter when not using, eg, Tweetdeck.