No event is required to introduce the Haswell MBPs. Most Mac introductions the last few years have been without an event. I cannot imagine Apple would schedule an event just to say that they've added Haswell, 802.11ac, and PCIe SSD to the MBP. It would generate the biggest collective yawn among the press at any Apple event in history.
I would normally agree with you but I think a 'Mac' event will happen because Apple has three items to show off:
-MP
-Mavericks
-MBPr
That makes a nice round number and each of these would be a boring event but together gives them a nice show.
Given that Apple is running MP ads in theaters, I doubt they are going to do a silent release of this which leads you to an event. By having all three product together you maximize your event millage...
-P