Decca Aitkenhead asked him about it briefly for her Guardian G2 series of interview/profiles - "He describes Justine as "brilliant", but feels no personal or political need to marry. "We'll get round to it at some point, but I don't think people would mind if we didn't." As party leader, he would guard his family life less ferociously than Brown, but more privately than Tony Blair, and "under no circumstances" will his sons go to private school - but that was about it.
But the explanation seemed straightforward.
In 2010, the type of newspapers which might think about going for personalised attacks on politicians involving their children would probably realise this would be rather more likely to backfire badly with their readers than to fire them up.
But no, the Mail on Sunday has decided to immediately get stuck in to Ed Miliband after all - "Ed Miliband becomes first British political leader of a major party to be living with his family out of wedlock" reads the headline online on its reporter Glen Owen's so-called news story.
You know, I suspect it will backfire rather badly with their readers.
Now Ms Thornton will feel the full glare of media interest in her style, behaviour and pronouncements.
adds the paper, slightly menacingly.
Well if the Mall is going to offer "the full glare of media interest in ... style, behaviour and pronouncements", perhaps we might gently reciprocate and inquire whether the newspaper has any plans to ditch the "Dacre Rules" over what women can and can't wear if being photographed in the paper, a Taliban-lite tendency entertainingly dissected by Rachel Johnson several years back.
"No black," she pronounced. "Dacre Rules. Sorry. Can you put on something else?" I scurried upstairs obediently to change. Emptying my wardrobe on to the bed, I settled on some jeans and a Cacharel shirt with a strawberry print. The photographer frowned as I came back down into the kitchen.
"No jeans," she said. "No black. No trousers. Paul Dacre only wants women to appear wearing dresses. If skirts, only to the knee."
But perhaps it is just a sign that Mail editorial overlord Paul Dacre is losing his appetite for British politics.
His dislike of David Cameron has rarely been carefully disguised. The Mail's risibly absurd class and foreigner attacks on Nick Clegg during the election campaign often simply brought mockery to the Mail, and now he has to deal with this Coalition nonsense.
And Dacre didn't even have the option of preferring the elder Milband to win the Labour leadership. It has been reported by Kevin Maguire that relations there were rather tense once the Mail decided it would be newsworthy (and no doubt enormously relevant to their political coverage) to try to buy the stories of the birth-mothers of David Miliband's adopted children.
Ah, the defence of "family values" ... I suppose that could be one word for it.