Engadget is pointing out how much of a "bag of hurt" it is having to log out of the Mac OS session in order to switch between graphics modes. This might be the case, but HybridSLI is a pain to use no matter the platform.
For example, take the Sony VAIO Z that is mentioned. That comes in dual-GPU flavor, but even when switching between modes you still need to close all open applications first. In fact, this put me off the VAIO Z enough not to get one.
HybridSLI has a lot of promise, but the drivers and associated software need a lot of work on both Windows and Mac OS.