Just why has Anna Wintour started to court publicity?

"And I try to give very clear direction to the people I'm working with. I'm not always warm and cuddly. I appreciate good work."

"Have you ever put anybody into a headlock?" he asked her to raucous laughter.

"Maybe you," she shot back.

The reception to this out-of-character love bombing has been bemused scepticism. She's trying too hard. She's desperate. What's she trying to prove?

I've lived in New York for the past 25 years and during that time have occasionally drifted in and out of the Wintour orbit.

I've met her a few times, once attended a dinner at her town house in the Village, and been to her pretty country house in Bellport, Long Island, as the friend of a friend.

I've dressed up twice and gone to her Costume Institute Ball at the Metropolitan Museum.

I've sat waiting in New York and in Paris for her entourage to arrive before fashion shows could start. I've seen her eating in trendy restaurants and caught sight of her at parties.

We're not friends, but we've chatted from time to time. I think she knows my name and I've always liked her. In private, she's relaxed and bright and chatty.

She keeps on top of everything, is well-informed and very funny - in that dry, sardonic English way that tends to hit the ground with a thud in much of the US.

I've often wondered whether her sense of humour could partly explain her reputation. Americans are often flummoxed by the British brand of sarcasm.

About a couple of months ago, I was at a Broadway play when there was a rustle of excitement as she slipped in and took her seat accompanied by her companion, Shelby Bryan.

The change in atmosphere was palpable and the mark of a real celebrity. Letterman said as much when she was on his show.

"I don't know much about fashion," he began earnestly.

"But I know you - and I think that means you're transcendent - that you're bigger than what you do for a living."

Anyway, like her or loathe her, there is a general feeling over here that she's no longer bigger than what she does, and she might even be past her sell-by-date.

Her annual Costume Institute party is no longer the go-to event of the year.

It's become an uptight corporate bun fight, with bussed-in B-list celebrities and bunches of tense not-so-cool girls skittering around with ear- pieces and clipboards.

The fashion in her pages is thought to be less edgy and out of reach as tame and out of touch.

The word on the street for much of this year has been that Carine Roitfeld, the edgy superstar editor of Paris Vogue, has sharpened her needle-thin elbows and is attempting to hustle Ms Wintour off-stage.

This partly explains the Wintour publicity onslaught of the past few months.

In addition to appearing on Letterman, she allowed herself to be profiled on 60 Minutes in an embarrassing interview with the octogenarian Morley Safer that you can still catch on YouTube.

"Vogue is the best of everything that fashion has to offer," said Ms Wintour in that interview. But fashion critics disagree.

The murmurs have long been that her taste is predictable (She hates black! And flat shoes!) and that she is becoming increasingly risk averse.

Vogue and Teen Vogue (which she oversees) are both losing circulation by double-digit percentages (15.1 per cent and 15.7 per cent, respectively).

Two imprints that she created, Men's Vogue and Vogue Living, have been shuttered.

This September's Vogue ad sales are down 36 per cent from last year's and fashion bloggers are predicting some kind of revamp in the magazine (hotly denied by Vogue spokespeople).

The question is, as The New York Times's Maureen Dowd asked in a column this week, Can she "stay relevant in a more down-market age and stay happy if she can't continue to throw away $50,000 photo shoots that are not up to her exacting standards?"

Clearly fashion's queen doesn't want to depart her throne. "What I really liked about the movie [The September Issue] is that it shows all the hard work that goes into making the magazine," she told 60 Minutes.

No one at Anna Wintour's Vogue works harder than its editor-in-chief. Her imprint is on every page and in every picture.

She has a devoted team who love and admire her, even while they grit their teeth at her insistence on having the final say.

Her loyalty to the "friends" as she describes those she works with at Vogue is reciprocated. She might be intimidating and she's never been a hugger, but her inner circle stands by her side.

Her children, Charlie and Bee, are grown but she has a close-knit family.

Bee, who graduated from Columbia University this summer is often seen with her mother at shows and parties but has no interest in a fashion future.

And what of Anna Wintour's future?

In The September Issue she is seen quietly walking alone, through the halls and into the elevator long after everyone else has departed and before they seem to arrive.

She looks less intimidating than lonely. And without the bright lights of the cameras she appears tired.

If she's having any fun, it's hard to see when or where. In these shots the joy and the glamour of the fashion world is completely invisible.

The editor looks like she needs a holiday or a massage or a nice cup of tea.

It's in these moments that one begins to understand why she agreed to the movie, and why she has been working so hard to sell herself.

Forget Anna Wintour's Vogue - she's Vogue's Anna Wintour. Editors will come and go but the magazine will survive.

Yet what will happen to Anna Wintour once she says goodbye to the gloss? Grace Mirabella, Ms Wintour's predecessor, was shown the door at the exact age Ms Wintour is now. Does anyone know where she had lunch yesterday?

"We're your glamorous girlfriend," Ms Wintour told 60 minutes in May, using the present rather than the past tense.

"When the time comes, will you go quietly?" asked Morley Safer. "Certainly," she replied, politely. "Very quietly."

Emma Gilbey-Keller is the author of The Comeback. She is married to Bill Keller, executive editor of the New York Times. The September Issue is released on 11 September.