I believe the defaults are implemented in code, not in .config file, if you look at the ProtocolMappingSection Class, method InitializeDefault with a tool such as Reflector or equivalent, you will see this:

protected override void InitializeDefault()
{
    this.ProtocolMappingCollection.Add(new ProtocolMappingElement("http", "basicHttpBinding", ""));
    this.ProtocolMappingCollection.Add(new ProtocolMappingElement("net.tcp", "netTcpBinding", ""));
    this.ProtocolMappingCollection.Add(new ProtocolMappingElement("net.pipe", "netNamedPipeBinding", ""));
    this.ProtocolMappingCollection.Add(new ProtocolMappingElement("net.msmq", "netMsmqBinding", ""));
}