The Monitor Calibration Assistant which appears when you click on the “Calibrate” button is part of the Default Calibrator, the software-only calibrator supplied by Apple. But the new calibration system is really a calibration framework, a plug-in architecture which can easily accomodate third party calibration applications. Developers can simply write their own calibrators as plugins to the calibration framework, and when the user hits the "Calibrate" button, a list of all installed plugins comes up. If you have an AppleVision Display or a ColorSync Display, Apple’s software Default Calibrator will not be available for use, since these displays have their own built in hardware calibration systems separate from the new calibration framework. As a result, you won’t see the “Calibrate” button on these displays unless you’ve installed a third party calibrator which does take advantage of the framework.
