I think the smaller-body models are built and braced to be more responsive to less attack, so they respond better to the light touch of fingers, while the larger models require a bit more attack, such as from a pick, to vibrate. Now, granted, there's a lot of overlap in the models and in players' attack, so the GA's, for example, are noted for being responsive to BOTH pick and fingers. And some famous fingerstylists, such as Leo Kottke and Michael Hedges, had no problem getting their dreadnoughts to sing. But, in general, the GC's vibrate more freely with a lighter touch, which is why they appeal to fingerstylists.
