Apple has never said, but a common presumption is that, when they thought about the panorama feature, they thought for handheld devices, the iPhone (can't recall if it's on the touch or not). When you think of a handy video camera, you think of smaller devices, not something bulky like an iPad. Although I will say I've been in national parks and Disneyland and saw plenty of people using their iPads as their cameras.
They probably used the same premise as they did with the Passbook app....who needs a 'handy virtual ticket' app on a bulky device like an iPad?
Nobody here can answer that with any certainly since only Apple knows why they didn't included the feature on the iPad.
The iPad is a tablet that includes a camera that was designed primary to be used with FaceTime. My assumption - and its only my assumption - that because the iPad is really too unwieldy to be used as a P&S camera, maybe Apple felt that the feature really want necessary on the iPad. I can't even imagine using Panorama on the iPad, and getting a nice clear shot with it.