I have two USB cameras, both of which are natively supported by OS X.1. When I plugged them in they would auto-launch the Image Capture application. However, now they no longer do, but ARE instantly detected. Ie. If I have the application already launched, it knows if they're plugged in or not. If I don't have the application launched, OS X.1's cursor changes for a few seconds when I plug the cameras in.
So it seems obvious that the OS detects them instantly, but refuses to launch the app, even though it is set to do so.