Don't buy that, buy this ... Richard and Judy, leading the books market. Photograph:Matthew Fearn/PA

James Robertson appears to be somewhat "conflicted", as Oprah Winfrey would say, about his selection for the Richard and Judy Book Club. While grateful that his novel The Testament of Gideon Mack, selected for the club earlier this year, sold many extra thousands of copies as a result, he worries that because people bought his book, they did not buy others.

That, at any rate, is one interpretation of a remark attributed to Robertson in the Herald: "The downside is that if someone goes into a bookshop and buys the books that Richard and Judy have recommended, perhaps they won't buy other titles," he said. "There is no doubt that there are winners and losers in this. That's something I feel slightly disturbed by."

The receivers of Richard and Judy's blessing have certainly been winners. Between 2004 and 2006, according to The Bookseller, the Book Club selections sold a total of nearly 12m copies, worth some £67m. Books such as Kate Mosse's Labyrinth and Victoria Hislop's The Island have been unmissable presences in bookshops: in the windows, on the front tables, in three-for-two promotions. It follows, naturally, that there are other books that have not achieved such success. Some books sell a lot of copies, and others sell a few: Richard and Judy did not invent that tough law of commerce.

They may, though, have exaggerated the effects of that law. Publishers and booksellers concentrate their marketing efforts on the books that are likely to generate the most turnover; increasingly, the rest are left to fend for themselves. The trend in the book market is for the haves to get richer, and for the have-nots to get poorer. Should Richard and Judy, some bookish types wonder, exert such influence over writers' fortunes?

The question arises not only from snobbery, but from unease that such life-changing selections are the responsibility of a small team, led by Amanda Ross at Richard and Judy's production company, Cactus. "There is a sense that it [the selection process] is very much about corporate dealing," James Robertson told the Herald.

We can dismiss this charge. Publishers both court Ross and - because she is so powerful - resent her, but have never suggested that she does not make decisions according to her own lights. There is more credibility in the related charge: that the list reflects Ross's middlebrow taste, just as the selections for Oprah Winfrey's Book Club - the hugely successful model for R&J - reflect Winfrey's enthusiasm for works that are "empowering".

When a book gets a book club selection, it is predigested for you, and offered as a work that fulfils certain criteria: strong storytelling, sympathetic characters, issues you can discuss at reading groups. Jonathan Franzen, whose novel The Corrections was an Oprah Book Club choice, felt that the Oprah sticker implied certain qualities that only coarsely approximated what he had been trying to achieve; his remarks prompted Winfrey to describe him as conflicted, and to cancel the show.

Franzen's fastidiousness is, to date, unique. More people reject knighthoods than decline a Richard and Judy or Oprah selection. These talk show hosts are the Edmund Wilsons, the Cyril Connollys, de nos jours: the most influential arbiters of literary taste. A few weeks ago, the reclusive Cormac McCarthy gave only his third interview since 1990, and his first television interview ever. To Oprah Winfrey, of course.