Bob,
One of the few sketches by Ross, not associated with any of this courses, is a sketch of many bunkers styles that were used. And that single sketch probably is not all inclusive and certainly reflects a style at 'one point' in time, discounting any evolution or change in style. Anyway, the original bunker sketch is in the Tufts Archives. The point is that there were many styles and Ross took the time to sketch out a few as examples.
From looking at the many old photographs, even though many people were employed by Ross, you can tell that there was some style and thought to much of the work. Have to believe that where Ross was responsible for construction, there was some expectation of the quality and to a great extent, the appearance of the work.
Look at the old photos of Seminole, Salem, Oakland Hills, Holston Hills, etc, to see some of the results. Oakland Hills and Seminole had amazing large flashed up sanded bunker faces. Salem had almost a rolled down face and Holston had semi-rolled down faces.
Today I think the ideas of the architect with the desires input by club officials (presidents, supers, pros, committee) is today's result. One aspect is often the clubs desire somewhat more difficult, deeper bunkers. The trend is also definitely towards less flashed up sand which many say results in less maintenance, as mentioned above.
As to the back wall aspect..............Today I think the trend is towards deeper bunkers, and in many bunker locations, given the terrain, the only way to economically do that results in a steeper and deeper back face. This is especially true when you have smaller bunkers, tight against the green.
Another result of this is that the bunker floor sand is often not as visible from the fairway or tee, which is a shame, but I guess you always know the bunker is there by the mounding.
Compounding the back wall aspect, is what I think is a trend towards firmer sand, which with firmer turfed faces, the firm sand results in balls rolling against the abrupt back faces. You just have to work the sand up just a little bit on the faces, keep it firm so the ball might roll a little back from the face. To help even more, rake the sand as much as was done with softer sands, you can lessen the amount of the ball rolling around in the bunker.
Overall, the YAGs bunkering is very pleasing. The only exception are the issues with those deeper bunkers where you sometimes have 'back wall issues.' This can be alleviated by a little TLC maintenance.