But how does a cross between the "Story of O" and a Harlequin romance sit with a generation of post-feminists who are in full charge of their careers and are unabashedly straightforward about their sexual needs?
After taking charge in the workplace and bossing the children around at home, women can be turned on by surrendering that control.
Bruni notes the trend is also seen in the new HBO series "Girls" -- a modern "Sex and the City," whose main character matter-of-factly enjoys submissive sex games.
Bold and aggressive Samantha Jones, she is not.
And Bruni asks, "Gloria Steinem went to the barricades for this? Salaries may be better than in decades past and the cabinet and Congress less choked with testosterone. But in the bedroom?"
Marion Solomon, a couples' therapist who coordinates mental health training at ULCA, said that even though women have made "great progress" in gender equality, biological models still prevail: strong male, submissive female.
She said the book is rather tame by bondage standards and mirrors an age-old fantasy among women. The psyche doesn't change, according to Solomon, author of "Love and War and Intimate Relationships."
For women, with so much on their plates, "they get tired of always being the strong one" she said.
"She won't be truly hurt," said Solomon, who notes that Grey gives Steele safe words to guide their sex play: "yellow" for caution and "red" to stop.
"What she is agreeing to is being with someone stronger and richer who feels safe," said Solomon. "We can ask how she let her herself get into it … but we always say women are trained to want men a little bit older, a little bit smarter, a little bit richer and a little bit taller."
Christian Grey is faithful to Steele with unwavering respect. And he practices safe sex, always using a condom.
But he is a badly damaged man -- with big-time mommy issues. His mother was a "crack whore" whose pimps extinguished cigarettes on the young boy's body. At the age of 4, he watches her die.
"Women are always drawn to men who are vulnerable," said Solomon, hoping they can save them.
"Human beings are like nested Russian dolls," she said. "On the outside you see a functioning adult. But [the dolls] get smaller and smaller until there is a tiny baby inside. We all have that."
And that applies to men as well. Solomon said she has seen just as many male clients -- "men powerful in business" –--who wanted to be taken care of.
But Stephanie Coontz, author of "A Strange Stirring," which examines the rise of feminism and the changing status of women throughout the 1950s and 1960s, said that although women have for centuries fantasized about submission to a dangerous man, it's a cultural construct.
"As a historian, I do not believe that women have some gene or evolutionary drive to be submissive," she said. "In fact, many women can be sexually aggressive."
She acknowledges that fear and submission have been the "staple of women's erotica" -- but not because their careers are so tightly wound that they need the sexual release.
"Women are susceptible to this not because of the power gains they have made, but in spite of them," she said. "For the last 200 years, the definition of male-female roles is that men are strong, silent and protective. One of the common fantasies is that you take someone who is so threatening and scary and find that the core in him is that he loves and protects you instead."
She said the book is a "classic case" of fear fueling sexual attraction.
"This has always been a disturbing aspect of women's history," said Coontz. "We're all creatures of a combination of sociology and biology and often adrenaline is easily confused with love and desire."
Rather than moving backward, she said women are feeling freer to "play a wide range of [sexual] adventures."
Katie J.M. Baker, a 24-year-old staff writer for the sex and celebrity website Jezebel, agrees that women are more open-minded about pornography.
In her column, "Is the Bestselling 'Mommy Porn' Book Worth the Hype?", she reports that some women were so excited about the book they were buying their husband's silver ties [Grey's signature ligature].
But she couldn't really see the how the book could be considered such a turn-on.
"It's really bad and I don't think it really appeals to younger readers," said Baker. "Besides, 'mommy porn' is a really gross term."
"It's really cool that women feel comfortable exploring their sexuality." But come on, she insists, "a 21-year-old virgin who has never kissed a guy?"
"It's a fairytale -- the same kind of princess and prince story -- with a twist," said Baker. "I call it hate reading. We read it, to make fun of it."