Smajdalf:
Another possible diode function: protect the caps from the motor. If supply is disconnected and motors are moved by some external force they will generate back EMF. If it is in the "right polarity", it will only charge the caps. But in the other direction it would damage the caps (or other parts of the circuit). The diode prevents this.
And any electronic components sharing the power supply, good thought.
The circuit shows two caps, probably, as mentioned earlier, they are positioned at different points of the PCB or circuit to help reduce noise, current surges.
Tom... 