Here's a bit from Jerome Weeks' interesting story in The Dallas Morning News on paperback "classics" lines:
"Shelf space in bookstores is at a premium," Mr. Hettler says, "and Modern Library has acquired a strong new position among the quality classics. It has forced the chains to make choices."
So some of this sprucing up [of paperback editions of classics] has been a defensive response. Classic lines are trying to stop incursions by the new imprints and re-prints.
All of which is a textbook example of business competition. Economist Adam Smith first explained such market forces in his 1776 classic, The Wealth of Nations.
Which you can find at many bookstores ? in a variety of handsome editions.
This story is worth keeping in mind next time the Eldred v. Ashcroft decision, which upheld extended copyright terms, comes up for discussion.