This follows a similar incident earlier this year in which 77m accounts were compromised. To give the company its due, it didn't make any rash promises about this never happening again at that stage and it doesn't seem about to sat any such thing now.
This serves to emphasise that everyone who puts their credit card details online is to an extent making them vulnerable to hackers. Sony is a non-trivial-sized company and if it can't offer better protection there's a chance nobody can.
Sony has put a note up on its site saying that the large number of customers with suspended accounts is pretty much a precaution and that only a fraction of them - less than 1% - will actually have had their details stolen.
Oddly it says the details were lost through some sort of third party. This is very peculiar because non-disclosure of details to third party sites is often a prerequisite for people signing up to this sort of network.