no, there are many staterooms that only sleep 3... they do not have the overhead bed.
All of the non suite rooms at least have the main bed (which can be split into two twins) and then the convertable sofa bed. Then there are some standard rooms that sleep 4, with the pull down bed above the sofa bed.
The family stateroom can sleep 5 , because it has extra square footage to allow for an additional pull out bed, which basically pulls out right in front of the verandah door.