Sounds right. And the defense would be two or three crewmen armed with M-16s somewhere in the back of that area, covered to withstand a grenade or two. They must see that nobody enters that area or climbs above it.
It's unfortunate that the outcome in this particular case was not the total destruction of the pirates. Somehow the attackers lost the element of surprise but otherwise they are up against what seems like a pretty soft target.
If those large cruise ships are steady, a good shot could make swiss cheese out of one of those boats and their crews at a good distance.
Also wonder what the legalities of having arms aboard a cruise ship in certain ports.