Corrosion is one of the main causes of faults on arcade boards. Home consoles are usually handled with more care and they have a plastic shell, making them less vulnerable.
Corrosion on PCBs causes copper and other metals to be "eaten up", cutting traces and connections between the components. Copper shouldn't "rot" naturally, especially since it's covered by the green soldermask. Corrosion can be a slow process, and is often caused by leaking batteries and spills.
PCBs damaged by leaking batteries can often be repaired by cleaning them and patching the broken connections.
In some cases, corrosion caused by spills can cut entire buses and even "climb up" chip pins, taking out 10's of traces and some chips.