I believe that pasture kept horses are best for both you and your horse. My horse is pasture kept he has no bad habits and is much more relaxed when I ride him. A stall kept horse can pick up vices such as cribbing, and pacing these are the result of bordom. A pasture kept horse has the option of running, playing, and foraging keeping them active, healthy and clean of unwanted habits.
I think this is great! I have always believed that keeping your horse as natural as possible (no shoes, clipping, blankets or stalls) was best, and this supports that even more! Perhaps that is why my little filly has progressed so much even though I only get to see her maybe once or twice a week most of the time.