In my current work place, we use CVS internally. Maybe, that is the reason for preventing the that port for external access. From what little I know, a version control system is another form of easy means to deposit data (versioned). May be, there exists a paranoid feaar that someone may start depositing versioned copies of compay source code! Not sure though.
Please try asking your sysadmins and tell us what they say. We need to know!