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 - Get Report) Kindle, the Barnes & Noble ( BKS - Get Report) 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.

Smith feels that most major publishing houses are now mature e-book providers that have captured major sales success and significant cost savings. The fresh terrain left, therefore, will be limited to areas such as textbooks that must present large amounts of knowledge in new ways,

"I don't think student needs are being met right now," he said.

A collapsing global e-book story
This uncertain narrative for the upside in e-books is made that much scarier by the sad fact that -- just like every more other information-based business in the digital age -- book publishing is a collapsing business worldwide.

"Lower disposable income hampered discretionary spending on books and, therefore, hampered global book publishing industry growth during the past five years, " summarized a June 2012 IBISWorld report called Global Book Publishing. The report totaled up the damage at an annualized five-year contraction rate of 2.5%, which included a 3.7% drop last year alone.

Worse, inside this declining market, once truly-hip e-book reading devices now must define themselves in a glutted global display market of portable PCs, tablets and smartphones.

Smith's daughter "reads physical books and digital books. There is nothing cool about either," he says. To him, today's kids feel books are simply everywhere. "It is how she reads."

And those challenges must in turn be addressed in an increasingly complex and crowded Information Age market littered with consumer options such as online games and film. Publishing houses face the new challenge of first-tier authors increasingly experimenting with self-publishing. And, in what may turn out to be the most insidious problem of all, there is a slow but steady decline in available real world retail book real estate, risking a dangerous loss of consumer touch points for books.

Barnes & Noble sent shivers through the bookselling industry when its retail group head, Mitchell Klipper, revealed recently in an SEC filing that he sold about two-thirds of his shares in the beleaguered book retailer in August amid dismal performance for the company.

Greenfield did agree that while some doomsday scenarios for retail sales are possible with books, there is also much to be sorted out.

"Suggestion engines, new forms of book-oriented entertainment and new ideas we don't know about," he said. "We are still in the infancy of digital book publishing."

"It can go either way."

This commentary comes from an independent investor or market observer as part of TheStreet guest contributor program. The views expressed are those of the author and do not necessarily represent the views of TheStreet or its management.