Yup, copyright wasn't an issue because producing books was expensive enough to discourage copycats. The original copyright act I'm referring to was passed in 1790, which was actually passed a year before the Bill of Rights was ratified (you know, freedom of speech and all that). There was a lot of contention around the Bill of Rights, with many saying they were self-evident and didn't need explicit protection, and I'm guessing the Copyright Act was similar in distinguishing what should be a regular law and what needs an amendment.
It was probably discussed in the constitutional convention, but probably dismissed since the constitution was intended to define and restrict government, not define what citizens can and cannot do. I think that's the appropriate scope as well, I'm just sad that we've let the laws get away from us.