Those output resistors ....
As Steve mentioned, you can put the regulators directly in parallel, inputs all connected together, grounds all connected together and each output connected to a low value resistor and then the other end of those resistors connected together as the output.
If you tried to connect the outputs of the regulators directly without the little series resistors, you'd have problems. If you have four regulators, each of them will try to set the output at a slightly different voltage, this variance being the normal manufacturing tolerance. The regulator that tried to set the output for the highest voltage (it might be only 0.1 volt above the others) will try it's best to supply all the current that the load needs by setting the output a tenth of a volt above the others. Meanwhile, the other four regulators see that the output voltage is too high and they'll throttle back and relax, trying to get the voltage to go lower ... and it won't.
Although simple, the disadvantage of using this method of series resistiors is that the regulatated supply becomes "softer", developing an internal resistance that won't allow the regulation to be as good as a single regulator. So, the circuits that use a hefty pass transistor around the regulator tend to work much better.
Dean