No, that's not how it works in industries like this... You do NOT store vital information in plain text - you encrypt it. If they'd had even a rudimentary encryption scheme, they'd look at least a bit better... a company should not be storing their customers' data like that. Especially if they are as big as Sony. Anyone with a basic knowledge of computer security knows that
If you are a large company, you have to count on being the target of an attack at some point, and protect yourself and your customers accordingly.
So... yeah, it is their fault. :/