NEW YORK ( TheStreet) -- As summer reading fades into the falling September light, it appears investors must bone up on a familiar tale. Yet another so-called Digital Age miracle -- e-books -- has hit its slow middle chapters. "To suggest that e-books have not been a success for large publishing houses is simply not the case," Jeremy Greenfield told me. "Their revenue has been incredibly resilient. It's not like what you see in music or newspapers." Greenfield is editorial director at Digital Book World, a New York online digital publishing industry news and conference service. And he has been explaining to me over the past several months the new realities of books delivered virtually on platforms such as the Amazon ( AMZN) Kindle, the Barnes & Noble ( BKS) Nook and various Kobo e-readers. In spite of that e-book upside, Greenfield has been blogging on the fact that 2013 has seen a decline in e-books sales in some categories, due to the lack of hits such as as recent years' The Hunger Games or Fifty Shades of Grey. Based on American Association of Publishers numbers he's familiar with, children's e-books saw revenues collapse by an Information Age-like 42% in the first four months of 2013. That drop was offset, in part, by a jump in adult and religious e-book categories of 8% and 12% respectively, which led to an overall flat 0.7% e-book growth. Jesse Chiang, an IBISWorldwide analyst based in San Francisco whose work I respect, confirmed for me in an email that while e-books continue to be a growing source of revenue, he projects that domestic e-book sales will slow in the next five years to 7.5% annually.
"This is in stark contrast to the annual growth rate in the five years to 2013, when domestic e-book sales grew 76.2% annually," he said. Tellingly, the sense of a more targeted upside story in electronic books is being felt by the industry's most entrepreneurial, self-avowed e-book nerds. "What you are seeing now is opportunities in unique parts of the e-book market," Michael Smith told me. Smith was both the former executive director for the International Digital Publishing Forum and chief technology officer for EasyPress Technologies, an online digital publishing technology provider in New York City.