"In the spirit of transparency". Right, Apple.
And the site was down, so it was clear something was going on.
It is also extremely transparent in the sense that people were wondering this exact thing even earlier today, and now received a response detailing that this is an extremely severe breach, as opposed to something else. What more do you want on a Sunday?
And announcing it just because people have started to speculate is damage control, not taking responsibility.
It's possible it took them a few days to figure out exactly what was taken and waited until they had as much info as possible to make a statement. I doubt Apple would be following blogs during a situation like this with someone making the decision: "oh, people have started to speculate about what's happening - I think we should make a statement."
And 'taking responsibility' means solving the problem. They have told us what they are dealing with. What more do you want from them?