Question with no answer - few CIOs move to become CEO?

First a quotable quote: "Librarians are being made CIO's less for our technical skills than for our organizational skills and our ability to manage the complex change that is fostered by or linked to technological change." [Source: Managing Technology, Managing Technologists, Shirley K. Baker]

An image tells a thousand words, in my humble opinion [image courtesy: blogs.idc.com/ie/].

"Knowing what we know about CIOs -- that is, that most are smart, hardworking, supremely aware of how the business works and increasingly savvy regarding the working of external customers' minds -- the failure of more CIOs to become CEOs has to be one of the biggest mysteries of our age. If any readers can shed light on it, I'd love to hear what you have to say." Thus spake Thornton A. May, in the Computer World magzine, March 2 2007, p. 10

Others who reflect on this paradigm:

THE CIO'S ROLE IN THE CEO'S AGENDA, By D. Neil Gissler,
11.11.2004 Cutter Consortium, special to SearchCIO.com

Interesting thread at Slashdot, based on a vacuous article about why CIOs don't become CEOs.

Why don't CIOs become CEOs? by Espen

Google for similar problem of moving up on the ladder.

Much more @ Google

DESKTOP COMPUTING - Help for Librarians, BY LAUREN CAPOTOSTO [Editorial - CIO]

Any comments?