I would say Exchange 2013 HA and site resiliency got into a matured state from the previous version of Exchange. Exchange 2013 provides multiple options for HA and site resilience. Microsoft has tried to keep human intervention to a minimum and allow Exchange to recover itself from any kind of failures so that the administrator can focus on recovering the failed hardware or server rather than recovering the service.
Below are the two articles by me on Exchange 2013 HA and Site resiliency
I hope you got some quick understanding on Exchange 2013 HA and Site Resiliency options 🙂