While online and self-service checkin is common in the US, I haven't seen many instances where the bag-drop portion is automated. Though it looks like that is beginning to roll out. Typically when you drop your bag in the US they insist on matching your photo-ID to your boarding pass. This hasn't happened at the self serve bag-drop points that I have used in Europe. Obviously, this could be done, by performing checks in the line along with the usual ICTS(sp?) checks that they tend to perform for US bound flights. However, the system seems to be currently set-up for single airline at-a-time per desk/group of desks. To really achieve the efficiencies that the airport would like, you need to move everything but special situations to truly common use, i.e. anyone can use any machine. A slightly less efficient would be group all the US departures together. Further, in the case of pre-clearance, if the system is similar to DUB they photograph your bag on check-in, and you are asked to match it in Immigration. I can imagine that some groups who are travelling together but not family could have issues with this part.
Bag photo's are a small part and can be done internally and don't require the passengers present as is done with transit passengers.
As for matching ID in the US, I expect this is most likely airline policy rather than US security policy as they are domestic flights and if strict procedures were not in place anybody could fly under anybody's name. Saving them from been fined. This wouldn't be a problem for Int flights.
Think you are over analyzing self service desks a little to much, any technology can take automatic photo's if the US really want them taken at check in.