Sheryl Sandberg, Facebook's chief operating officer, made Fortune’s Most Powerful Women list again this year. (Spencer Platt/GETTY IMAGES)

Quick: Which industry do you think is most represented on Fortune’s annual Most Powerful Women ranking? Retail? Apparel? Consumer products?

If you guessed any of these, you’d be wrong. One of the most interesting things about this year’s list of women at the top is how many hail from the technology sector. There’s Ginni Rometty, IBM’s CEO, at No. 1. Hewlett-Packard’s Meg Whitman, Facebook’s Sheryl Sandberg and Oracle’s Safra Catz all show up in the top 10. In all, no industry appears more frequently on the list of women than technology companies, which hold, by my count, eight of the 50 spots on the list.

Surprise, surprise. An industry we tend to associate with male-dominated engineering teams and computer-science geeks produced more powerful women this year than any other industry did. This despite the fact that the National Center for Women & Information Technology reports that just 18 percent of 2010 Computer and Information Sciences undergrad degree recipients were female, or that just 25 percent of the computing workforce was female in 2011.

Meanwhile, female representation on boards in Silicon Valley lag the broader market, according to executive search firm Spencer Stuart. Just 9.1 percent of directors on these boards are women, compared with 16 percent of directors at the average company in the Standard & Poor’s 500-stock index.

Of course, a good number of these top women are not engineers or computer scientists, but the marketers, sales mavens or MBAs that help run the company. And that, says Debra Germaine, the managing partner of the technology, media and telecom practice at executive search firm CTPartners, may be exactly why we are seeing more women at these levels.

Technology companies are becoming more and more dependent, she told me in an interview, on people with sales and marketing backgrounds who can help bring a technology idea to market and who really understand consumers’ needs. Plus, she says, there is an increasing emphasis in technology companies on the services side (where there is often higher profitability) rather than the device side, and tech services tends to be a place where there are greater percentages of women.

“I believe it’s a function of women in roles that are driving the product into the market,” Germaine says. Little wonder that IBM’s Rometty—who helms the country’s 19th largest company, managed the acquisition that launched the company’s services business and holds a computer science degree—is No. 1.

There were some other surprises on the list besides the number of technology women. The aerospace and defense industry, also not traditionally a bastion of female leaders, had five women on the list, including three from Lockheed Martin alone. Financial services and banks contributed another five women. And one particularly famous woman who has long shown up on the ranking—Oprah Winfrey—nearly fell off of it. She dropped 34 spots to No. 50, as OWN, her joint venture with Discovery Communications, struggled.

More from Jena McGregor and On Leadership:

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