It seems as though something was recently changed in ES that changed the photo ordering. Take for example, in my avatar album you can see that the oldest thumbnail shows up first:
http://test.peakbeta.com/photo/item/2-avatar-photos/user/joshlewis
Same goes for story and cover photos:
http://test.peakbeta.com/photo/item/5-story-photos/user/joshlewis
On the other hand, showing the oldest photos for the rest of the albums makes a lot of sense. Consider if someone posts photos from a party, an adventure, or other various activities. People often want to see things in the order that they happened in. The only reason to exclude the cover, profile photo, and story photos is because they are not chronological (usually), hence people actually want to see the current you. Facebook does this because it would be more confusing to the viewer if done differently.