These are the results of the limitations of the medium, not the goal of the photographer. If publishers could get a transparency that would, better than today's transparencies, simulate the colors, clarity, texture, etc. of the original medium, they would jump at it. I also believe this statement misses the point of Bridgeman. I would think copyright law is interested in what the objects look like. How one gets to the end result, the copy, seems irrelevant.
Patents are for processes, copyrights are for the final execution, the result.
The often repeated issue of controlling access is the ultimate issue. Obviously there are many legimate questions to the practicallity of providing proper access. The current reality however, is disturbing. Many museums will prohibit access to public domain works to the point where the public can in no way take advantage of its rights. For example, if you were to go to a well known musem in New York and ask for access to say, a pd painting from 1520, with the idea that you would reproduce the work onto 5000 posters, the museum would likely refuse you access to the original and even a transparency, regardless of any money you may offer.