An annual gross income of 70k comes to approx 45k net a year, or 3.8k a month. So there is the first 25k gone, it's income tax. (guestimated figs based on own situation).
Then most of those families will be double earners, so be running two cars and pay towards childcare. A mortgage of 1k sounds about right as well. I don't think you should underestimate how much of that 3.8k goes straight away on regular bills, cars/petrol and other necessities.
We are in a similar situation as the people in the article. I wouldn't say we're struggling, it's a financially secure situation and with a bit of planning and sensible spending, we can buy all we need with money to spare for savings/days out. However, it's also not the kind of money where you can spend without thinking, live in a huge house, take fancy holidays and assume the cash never runs out. On that income, the goverment expects you to give, not receive, and in a way, that's a fortunate position to be in.