Sarah Sands: Michelle's front-page power is all in her warmth

Magazines sell on the immediate appeal of their covers. If you were choosing a significant figure this week, you might consider Steven Chu, the US energy secretary. Then quickly pass over his photograph.

The editors of glossy magazines make tough business calculations. The brave editor who defies commercial orthodoxy is very likely to be the fired editor. When editors hit a winning streak – such as the sales effect of Kate Moss – they stick with her through thin and thin.

It was with a heartfelt commercial sigh that these editors justified their reluctance to put black women on the front of their magazines. They just wouldn't sell. Women responded emotionally to faces on the cover. And for all the will and education in the world, white women could not bond with black cover girls.

Yet earlier this year Anna Wintour, editor of American Vogue, never one to be accused of soppiness, confidently slapped Michelle Obama on the front of her magazine. Since then, I have noticed that photographs of the First Lady have the same premium value as those of Angelina Jolie.

The rating system is not explicitly discussed by newspaper picture desks, but one knows a commercial halo when one sees it. Newspapers also demand that picture-worthy subjects must have an unpredictability. Kate Moss and Madonna understand the importance of constant renewal. This is fine if you are in entertainment or fashion. If you are in public service it is harder to be consistently arresting.

Now, most newspapers, most weeks, are on the lookout for pictures of Michelle Obama. Even in the midst of Cannes, executive heads turn at the sight of her. She has escaped from the foreign pages, even in the red-top papers. Eighteen months ago, I was in America reporting on the presidential candidates. My former newspaper was avidly and prophetically interested in Michelle Obama, but I could not share the enthusiasm. Surely it was her husband who had magical properties. She was merely his large-boned, rather stern wife. I took soundings from magazine journalists on her fashion sense. They shrugged and said that it was unexceptional.

That was then. Now Michelle has achieved a status as First Lady that we have not seen since Jackie Kennedy. The overwhelming difference between the two women is warmth. Michelle began warm and ended up with an almost Pentecostal effect on those around her. She is clever and practical, but her charismatic characteristic is her physical touch. She has a universal empathy.

In an interview in Time this week she explains it is how she stops people from being intimidated by her position. "I'm so touchy with kids, because I think if I touch them and I hug them that they'll see that it's real."

She extended the same courtesy to the unintimidated. I have done extensive research into the who touched whom episode at Buckingham Palace and can confidently state that it was Michelle's arm which shot out first across the Queen's back.

Our own Lady of the Hugs was Princess Diana, but there was a neediness in her embrace that does not exist in Michelle Obama. The strongest quality of the Obamas is ease.

An American political journalist explained to me that Washington has joyously adapted to the sexy happy couple at its centre. There are cocktail hours and friendships at the White House now. Everyone wants to be touched by the Obamas. Of course: they are magazine cover stars.

Sarah Sands is deputy editor of the London Evening Standard