Why does the General Account need the Replicate Directory Changes and Manage Replication Topology rights.
Replicate Directory Changes Right - The account needs this right to be able to use Active Directory's Directory Synchronizer (ADDirSync) Control, which allows for retrieving all changes since a particular moment of time.
Manage Replication Topology Right - The account needs this right for the QCS Tomb Stoning Mechanism to be able to retrieve information on when a particular objects attribute was changed.
Please also see the following additional KB articles:
What permissions are necessary for deploying Collaboration Services for Exchange?
Mailbox test fails: It is not possible to check the mailbox configuration, Error codes 32623 and 32622 appear in the event log