Continuus zooming has nothing to do with multitouch. It only has to do with the fact that classical mice and APIs implement scrolling through a stepping/button mechanism. I have a Logitech mouse that can do continuus scrolling just as good.
It's worth mentioning that the original mouse wheel API by Microsoft was explicitly written to support analog wheels. But it never took off, and it was actually the applications themselves who were ignoring the analog input and just converting it to a step.
Having used a mighty mouse which has a miniature trackball for a mousewheel though, I'd disagree about it being equivalent though, for the simple reason that dragging fingers on a small wheel or ball with real inertia is more restrictive than on a large free flat surface with simulated inertia. Particularly being able to fling at high speed and then catch it again, stopping on a dime, is actually a really fast way to get around.
Of course, it's only the confluence of good hardware, drivers and applications that makes this shine, and on that point we agree. But it's undeniable that Apple has an amazing lead on this, and using a magic trackpad on OS X feels like the biggest upgrade to how I interact with a desktop since Exposé.
