I'm not sure about why they'd be on a Dragon's lair, but in pinball machines they add a capacitor to all of the switches to lengthen the pulse sent to the computer pcb. There's also some on the coin switches of a Pac-man machine. Basically some of the old ic chips on the old boards couldn't 'see' a switch closure if it was really short... so they put a capacitor on it that makes the pulse larger and the chips can see it more regularly. So that's probably what's going on with the pcb in Dragon's lair that handles the inputs.
It may have something to do with 'debouncing' too. If you press a switch, it actually sends like 15 signals to the pcb... all really tiny as the switch makes good contact, loses contact, makes contact again, etc. In pinball machines they code the game so that the pulse has to be at least "......." long or whatever, to ignore if a switch is pressed twice within a tenth of a second or whatever, to get rid of this. Without it, each switch would score like 15 times each time it's pressed once.