While one could increase the resolution of the display to make up some of the difference, it is meaningless unless your tablet also includes sandpaper, so that the user can sand down their fingers to around one-quarter of their present size.
Apple has done extensive user testing on user interfaces over many years, and we really understand this stuff. There are clear limits of how close you can physically place elements on a touchscreen before users cannot reliably tap, flick or pinch them. This is one of the key reasons we think the 10-inch screen size is the minimum size required to create great tablet apps.
