After the mess that was the Wii U reveal, (and the Xbone one), this would make sense. Get a clear advertisement out that looks exciting but is also direct in its messaging and answers most of the important questions. Not an event that tries to create some kind of enigma, but reporters start writing conflicting things and then you have to explain but things get heated and you have to retract or waffle around certain topics. Just the controlled message, this is it, and only then do we invite people to try it out.
They just need to start a countdown timer two or three days before and eh presto.