Microsoft Exchange Server 2013 provides administrative functionality and other enhancements that improve the overall management of Transport Layer Security (TLS). As you work with this functionality, you need to learn about some TLS-related features and functionality. Some terms and concepts apply to more than one TLS-related feature.

What is the difference between Exchange 2010 and Exchange 2013 TLS?
There is NO difference , it works the same. It uses the same Opportunistic TLS mechanism.

So what is Opprtunitics TLS by definition from TechNet?
Opportunistic TLS In earlier versions of Exchange, you had to configure TLS manually. In addition, you had to install a valid certificate, suitable for TLS usage, on the server running Exchange. In Exchange 2013, Setup creates a self-signed certificate. By default, TLS is enabled. This enables any sending system to encrypt the inbound SMTP session to Exchange. By default, Exchange 2013 also attempts TLS for all remote connections.

My previous post about MS Exchange 2010 TLS

Resource URLS
Exchange 2013 TLS Functionality
Exchange 2010 TLS Functionality

Secure messaging is simple too.