Its argument is simple: it's not blocking you from using any videochatapplication you want, but it is exercising its right to manage the doors through which all chat applications can and can't be used.
An online videochat, using an application like iChat or Skype, starts like a phone call: one person requests a conversation, and the recipient must accept the request.
Now imagine that your application is a videochat app that is riding the Facebook wave, leveraging their social APIs, and has been fully backed financially by just one man.
Then a light bulb went off: What if he came up with an application that would allow him to videochat and instant message with people who might know the answer?