A law professor from University of Illinois prepared this chart. What it is showing is that the expanding copyright has actually limited the sale of books from a huge time period of American literature. There are actually about twice as many books sold that were written in 1850s as were written in the 1950s.
It is unfortunate that there was actually some meaningful copyright reform work released right after the election by the House Republicans. I was prepared to write up a very positive blog post about it. But in less than 24 hours the House Republicans withdrew the proposal and shortly after the man that had done most of the work writing it up had been fired. It is too bad. The point of copyright is to encourage the greatest good for producers of artistic works. But a copyright that protects a very small group of artists and the vast majority of artists languish out of print.
I am sure most writers want their books to sell millions of copies and for them to get rich. But most books are out of print fairly quickly, and apart from digital sales (which really are brining a lot of books back to life) most books are completely unknown. So if given the choice between no one reading my book and someone reading my book, but me not getting any income from it. I think I would choose the shorter copyright term and have someone rather than no one read it.