Well, you could argue that Apple hasn't done a tablet PC. They've done a tablet-sized phone. Of course, where you draw the line between those is probably different for different people.

They did, just not in terms of the underlying concept. The sheer size and weight of the iPad was innovative. Doing away with a physical keyboard altogether was innovative. Using a capacitive touchscreen for a far more pleasant user experience was innovative. In short, many small innovations rather than one big one.