Exchange 2013 has only two roles and the protocols handled by the roles are different to the ones in 2010.
In 2013, all types of clients connect to the CAS role. Rather than explaining all the types of access, the below slide from the recent TechEd session by Scott Schnoll shows the client protocol architecture in Exchange 2013.
Clearly, a picture is worth a thousand words
--> No more Hub, No more UC, things will be eased for deployments... please see the blog : http://www.howexchangeworks.com/2012/09/client-protocol-architecture-in-exchange-2013.html