A survey by the European Commission has found that parental control programs aimed at keeping children safe online do not function well with Web 2.0 sites, smartphones or games consoles... this at a time when 31 percent of European youngsters access the Internet on their mobile phones and 26 percent go online via game consoles. In addition, content from Web 2.0 sources like social-networking sites, forums, blogs and instant messaging also frequently slipped through the safety net.[ From "Parental Control Programs Perform Poorly With Web 2.0 Sites" on PC World (emphasis added by me) ]
Not really surprising. In fact, I would suspect that some of the success that any of these kind of functions may have with traditional ways of accessing online material is due to the stronger emphasis on the problem areas by web developers/designers. That's where the money is so that's where the content is. And efforts to block content might be an issue that developers might not really support.