Cocoa isn't built on Carbon Events. That was the entire point of some of the previous posts. Cocoa uses its own event handling code (look at the Apple docs that explain how the system fits together... you'll find that the event dispatch mechanism differs for Cocoa and Carbon).
Apple *have* used Carbon to implement some of the Mac OS X Cocoa methods, but it isn't used from the ground up as your comment implies. They have also (helpfully) made it so that you can mix Cocoa and Carbon code in the same application. But that doesn't mean Cocoa is built on Carbon... it isn't; sure, some things use Carbon (NSMenu is a good example), but not everything does (which is why Cocoa apps behave subtly differently in many cases).