If the claims that they ignored warnings are correct, I would indeed lay most of the blame on Apple:

http://iphone.appleinsider.com/articles/14/09/25/researcher-...

It may be the case that celebrities chose poor passwords, but how can you blame them? Did Apple enforce strong passwords? Did it allow an excessive password retry rate? Did it fail to follow up on warnings from security researchers?

Unless the answer to each of those questions is "no", it is entirely fair to blame them.