Transformer is there to handle worldwide voltage supplies. The secondary is 100VAC, the common Japanese supply voltage (50 or 60Hz depending on the area), and the primary is tapped to handle 100, 110, 120, 127, 200, 210, 220, 230, 240 and 250VAC as a supply voltage, and is sized so it will operate with low loss on 50 or 60Hz mains. The isolation is there to reduce the chance of injury to the public if the top light cover is broken by accident by an over enthusiastic player ( common thing) or the CRT is broken while powered and somebody falls inside or shoves a hand inside. Does mean you have to be careful in replacing the lamp, and starter as you need to use an Osram ST151 or Phillips S15 starter, otherwise the lamp will not light, and the ballast choke has to be the right one meant for 100VAC operation.