Indeed many people including Dalton were saying that from 2007-2011ish when the Twitter API was wide open and speculation about it's potential as plumbing ran rampant. However over the last few years, it became increasing clear that the contingent of people inside Twitter who saw it as new and amazing plumbing for the next generation of applications were losing, and the contingent who saw Twitter as a media company selling advertising with a fully controller and branded user experience were the ones who won out.

Anyone building an app on top of Twitter for anything other than personal or experimental use is a fool. Unfortunately for anyone building on top of App.net, it doesn't have the users to make it broadly interesting or significantly profitable.