In my opinion, the big 2 insiniuates more than a spec upgrade. Apple never gave their babies new names unless they had some big improvements (iPhone 3G->iPhone 3GS). Same with firmwares (3.2->4.0 etc.).
Also, the event will be all about iPad 2. How can they fill time with saying "And now, one more thing: 512 MB RAM!!!"
The iPhone 3GS did not really get much time in the event, just some screenshots, data and not much of a hype. Same with upgraded MacBooks and stuff - they are not the main thing of an event
We will see a Ipad 2 and a a preview of IOS5...