Then Microsoft completely altered Skype's design (from supernode/P2P to client-server) making it cost a LOT more to maintain while offering no obvious advantages, which more or less confirmed it.
Quote from Microsoft PR on the change:
As part of our ongoing commitment to continually improve the Skype user experience, we developed supernodes which can be located on dedicated servers within secure datacentres. This has not changed the underlying nature of Skype’s peer-to-peer (P2P) architecture, in which supernodes simply allow users to find one another (calls do not pass through supernodes). We believe this approach has immediate performance, scalability and availability benefits for the hundreds of millions of users that make up the Skype community.