Exactly.
Lots of events include more than just a single product or announcement. Seems silly to book the time and space and just say "new iPods...that's it. Okay, bye!"
Sure, the chances of a new notebook are slim, but you never can tell. And even if one doesn't appear, nowhere does it say that this September 5 event is "all iPod". It could have some iTunes or tv-related news.
In fact, I can't recall a single Apple media event that was about
one product only. That never happens.