Most of us, even English majors, make grammatical mistakes. The difference between a copy-edited book and one that has not been copy-edited is enormous. Copy-editing doesn’t change the substance of what you’re writing about. In fact, it enhances it – clarifying meaning, correcting distracting mistakes.
A good copy editor will adjust your punctuation and spelling, question whether or not you really want to use jargon, make sure you’re using the right terminology, and keep you from embarrassing errors of usage. He will keep your language consistent from page to page, and ensure that you capitalize names properly.
The ISBN was invented in the 1960s, when British bookseller W. H. Smith began computerizing its distribution system. It became an ISO standard in 1970, and now the ISBN forms the backbone of the book supply chain around the world. Certainly there are plenty of books published that do not have ISBNs. Proprietary publications that are not traded, for example, don’t require ISBNs. Books that are sold in “walled garden” environments don’t require ISBNs. So why use them?