The retail distribution networks have put content into the hands of "the general public". It has become economically viable to distribute content by having the customer come to some retail outlet that orders many copies of various kinds of content and allows the customer to purchase them and take them home. Much like the postal service, this required the invention of reliable transportation and a large enough customer base to sustain the retail outlet.
And much like the postal service, only more so, this has affected the law by affecting everyone, not just some select group of people with convenient access to content in a copyable form. Perhaps more then anything else, the developments implied by the large scale distribution of content in retail stores, put together with the need for consumer technology such as VCRs to use this content, has brought this down to the level where the decisions made regarding these issues will affect everybody in their day-to-day life. What can I do with this CD? Why can't I send my friend a quote from an electronic book?
The existence of a large-scale distribution network for some kind of content, like sound recordings, tends to imply some sort of standard medium for distributing that content. As more people own players for that medium, the technological pressure to create technology to allow the mass-market consumer to also create content on that medium increases. Thus, a few years after the introduction of the CD-ROM, we get mass-market CD writers. DVD writers arrived even more quickly then CD writers did, relative to the initial introduction of the medium. A large-scale retail distribution method by its very existence tends to create market pressure for the creation of technology that will be capable of allowing the user to, among other things, violate copyright laws.