The quality of foster homes varies with locality, too. Bad foster homes are more likely to slip through the cracks the more overworked the people in charge of oversight are. There are some very, very good foster homes, and there are some very, very bad ones. The thing is that I'm not actually too worried about this kid. He's got media attention, and he's got a mother (who, most importantly, has a lawyer) looking out for him. You bet they're going to pay attention to how he's treated. The kids that I feel bad for are the ones that are in foster homes with no media coverage, no parents that care, and no hope of getting out of the system.
And it's significant that they didn't just pop this boy out of his home and put him in foster care - they worked with the family for at least a year before they took him away. It's one thing to decide for yourself that you're going to lose a few pounds (or a lot of pounds) and then backslide. It's another thing entirely when it's, get the whole family losing pounds or you're going to lose your friggin kid. Additionally, I don't think this case sets a terrible precedent. In cases of gross negligence, which this is, it's appropriate to remove the kid from the home and try to get him some help. I think that the parents should take nutrition classes before they can get the child back, too.