I dont think hiking requires training, especially when your hauling super light loads like the people on this site. I see lots of hefty people on the trail. Hiking is not strenuous in my opinion, it can be at times, but other times it can be very easy. So i dont think you need training to be good at it, however, you should train just to train, for your health. I seem to do the same miles regardless of how good of shape im in. I dont like doing 20 miles a day, i like exploring, if i hear a waterfall but cant see it, i like to bushwhack til i get a view. Otherwise i would miss everything.
I think hiking is more about conditioning. Conditioning the skin of your feet to be tough, your hip bones to absorb shock, your body to take to extreme temperatures more easily.