I know in Australia we are on 230v system and most residential outlets are 10A and so on.

The game could be at peak - say in a multiball using up to 9A which would leave 1A available. If say the service outlet was consuming 2.5A and then the game hits it's peak a brief reset of the computer board may occur...

Also from what I have been told the service outlet is always on so not idea as when the machine is off the service outlet si still running / on.

Service outlet is on when the game is turned off. This is for repairs.

Probably so you don't have the game turned on and plug a vacuum cleaner into the service outlet, and melt the cord between the game and wall outlet.

LTG : )

Is the varistor wired before the service outlet?
If so, maybe the varistor is something that would also melt.

Nope. In WPC games, nothing is ahead of the service outlet except for the cord connection in the back of the cabinet.

I've actually plugged in a vacuum before and even another game into the service outlet and never had a problem. Obviously the game whose outlet I was using was off.

I can't think of anything that would limit the current to 2A as the fuse rating after the service outlet is 8A.

You basically answered your own question. It's suggested to limit the current consumption on the service outlet to less than 2A, because what ever you are plugging in is X amps + the game draw max amps (if it is on) and you could melt the wiring, exactly as Lloyd stated, because there is no fuse ahead of the service outlet.