I hate to say it but:
(a) Australia has, so far, been kept well clear of terrorist activity and
(b) Virgin Blue is a new, naive airline without much experience
Please remember, Mohammed Atta (the pilot of one of the World Trade Centre airliners) was a Business Class passenger accepted after flight closure! (You can just imagine him saying "I must have an aisle seat near the front!")
Unfortunately for the majority of our passengers, that is the reality of the situation and why all airlines must continually be on guard - particularly as regards late "runners"!