Sony knew about the problem for ages and ages.
That's why it only affects a certain batch made between certain dates... because Sony discovered the problem and stopped production. The reason they sat on it until now was because they could save money by waiting until people complained, rather than force a full, immediate recall.
Now that they're paying out a bucketload to everybody... if the PS3 fails then Sony are on the Bankrupt Express if you ask me. Too big for their boots with nothing to show for it.