Per the MA 4.5 release notes:
Communication security enhancements
When used with ePolicy Orchestrator 4.5, all agent-server communications are encrypted with Transport Layer Security (TLS), the industry standard high-encryption protocol.
Communications include the following:
•Update Now actions
•Authentication and authorization
•Bulk data transfers
Port 80 is used for http transfer of the above.
Port 443 is used for ssl transfer of the above.
The use of http or ssl is chosen globally by the ePO server setting - ports.
The content is the same in both cases, only ssl is more secure.