The problem with statistics like this is that too much is assumed. It doesn't take into account the differences in modern lifestyles and situations. There are so many single-parent families now, and even in two-parent homes, work schedules often prevent the "classic" meal schedule where everyone is together at mealtimes.
Even school schedules get in the way. My girlfriend's two kids go to an early shift where they get breakfast and lunch at school, but we both work later shifts and don't get home til after 9 pm so the kids eat dinner at daycare. The only time we can actually have meals as a family is on the weekends.
I love to cook, and I make most things from scratch, so we wouldn't need to spend a lot of money on convenience foods, but we do use them so that the time we do have to spend with the kids isn't taken up by a lot of cooking time. We know the kids get balanced meals at school and daycare, so we just grab something quick for ourselves. I think that's the way for a lot of people, so the food budget gets a bit higher and nutrition takes a hit for us at times.
To answer the question, including what we spend on meals for the kids outside the home, our food budget is about $150 per week for the four of us. If we could have the standard breakfast and dinner together at home, I could probably take $30-$40 per week off of that and we'd eat better.