They are inviting the media and people such as Serenity Caldwell, i don’t think they would do that if it was just a short event about updating a couple of services like iBooks. I think we are likely to see new cheaper iPads and maybe the rumoured cheaper MacBook Air or MacBook with Retina display, the Air is used a lot in
eduction by students and teachers.
Edit: the editor in chief of the Verge has also had an invite to the event.
I'm sure they invite all of these people to every event. Thats what the events are for - free PR.