I wonder why they announce the arrest if their not prepared to say anymore or confirm the name? maybe they shouldn't announce the arrest at all then? or is that against the law and they have to announce or confirm they arrested someone as a legal measure?.
I'm not sure. The name usually comes out later in the day, doesn't it? Perhaps it's to do with police procedure? (Checking it's the right person, checking the accusations were against them and constitute a crime having been commited etc etc., making sure the paperwork is in order.)
As I've said before - a false accusation of something like this would be awful, but ,on the other hand, releasing a name can encourage others to come forward with information.