As this question comes up over and over again, I wonder if it's better to think of it like this - there is no Exchange Agent. Nor is there an SQL agent, and so on. Just a remote agent for Windows servers. (I'm excluding things like the Mac agent and the Linux agent for simplicity).
When you buy a remote agent license, you unlock the ability to backup one remote server.
When you buy the Exchange agent license, you unlock the ability to backup one Exchange server.
When you buy the SQL agent license, you unlock the ability to back up one SQL server
...and so on.
Sometimes I feel the terminology used by Symantec (and Veritas before them) is what causes the misunderstanding.