As Godin says, they started years ago. Apple is one of the only companies in the world with not only the power to set up limits on access on a device this big, but also keep a rabid fanbase hyped and waiting. Apple has created an image designed exactly for releasing products like this, with the secrecy and speculation and announcement events, and so on. And the company has backed up that image with pristine engineering and design -- as Godin says, rather than be everything to everyone, it promised a few things to a certain group of people (the iPad can't do Flash or multitask or take pictures), and then delivered (but it can do the things it does really, really well).
And perhaps most importantly, when launch time came around, Apple's management didn't focus on "launching," they focused on simply getting the product into customers' hands. The iPhone had all kinds of issues with setup and purchasing and activating and so on, but Apple went out of its way during the iPad launch to make sure customers had the iPad when they were supposed to --waived shipping fees, plenty of inventory in stores, and a push for delivery at exactly the right time. That's how you make $150 million in a day: Promise what you'll deliver, and deliver what you'll promise.