Having the same features is not the same as interoperability! Ultimately people use the AIM network and AOL receives no net value. They can use any client and

Having the same features is not the same as interoperability! Ultimately people use the AIM network and AOL receives no net value. They can use any client and the data is private. Additionally they can migrate between clients because their network is a part of the protocol. That the messages are public is completely relevant. As long as the twitter network is used, twitter can create value from the data. Twitter search only grows in value when more people are on their network. This is why the comparison between AIM and Twitter is flawed.