I don't think that you have fully explored the potential for this article. If you did full a feature comparison it might shed more light on the topic.
For eg, Big Brother CAN do "real time" monitoring via snmp traps and reporting via LARRD or Butter. It cal also do SLA reporting which I don't think that any of the other OSS products can do.
Also one HUGE advantage that Big Brother has is that it has agents for windows and other nix..This way you can do NETWORK and SERVER monitoring from the same console. Just checking ports up/down doesn't cut it any more.