In the example above, the load is distributed to the supports by using half of the span between the support. Each tributary area of each joist is half the span to the next one on each side. In a system like the one illustrated, you can also use a load factor reduction, assuming that if one member deflects too much, the load transfers to adjacent members.
An aircraft floor deck is a composite system, meaning everything is attached in such a way so the that everything works together, it acts like a giant plate truss, distributing the load among all of the stringers and purlins/sub-purlins through the members and the decking. That is why it is so strong.
Pallets are considered sacrificial. They are used to transport the load, but also to make sure there is an even contact area for the load. Deliberately rigid and flexible. Note that when loading, the pallet jack wheels concentrate the load on a very small area, and this is acceptable
You need to start looking at the load being a concentrated load when it is large load near the loading limits in a small area, usually at or near the rating.