I think just from reading mumsnet you can see it isn't an unbelievable figure. How many people would describe their parent as being distant or emotionally unavailable? Or not really seeing their children as separate people? Or quite selfish and narcissistic? How many posters describe themselves or their partners as being afraid of commitment, or jealous, controlling, clingy or needy in relationships - where do you think these patterns of behaviour come from? Add in all those people who had mothers who were depressed, had PND, were ill for an extended period when they were young, had alcohol issues, suffered family breakdown or DV? Some parent styles advocate being unresponsive to a child's needs - plenty of posters report midwives or MILs telling them not to pick up the baby when it cries or you'll spoil it, show it who's boss, babies are manipulative. That's even before we talk about children who were abused or neglected or in care.
I spent last weekend with a nice, professional, married couple who obviously loved their toddler very much, and he was well fed and cared for. However they felt strongly that babies shouldn't be mollycoddled and mustn't learn that if they cry someone will come to them etc. Already at 2 you could see the child had a insecure attachment style.
An ex-partner of mine had an avoidant attachment style - he doesn't display a lot of emotion, he can be distant, reacts to stress by withdrawing, tends towards being a loner. His mother had very severe and largely untreated PND after his birth and until he was 2 or 3 really, and although she did a great job caring for him she found it hard to bond with him in his early months.
The OP asked about what a good attachment looks like, and from her posts it sounds like she has it - she responds to her children's needs, is sensitive to their emotions, and they are confident to explore or go to others while still looking to her as a secure base.