I'm seeing them everywhere at the moment, and I thought they were banned or something?

I go jogging in a small park down the street from me, which gets about an even mix of kids in tracksuits and yummy mummy families, but all of them have staffies. Seriously, probably about 80% of all the dogs there are staffies (the remaining 20% are oh-so-fashionable pugs). I appreciate that most people round here (south London) won't have much in the way of space so I understand not seeing loads of German Shepherds and Labradors knocking about, but I never knew staffies were so popular. I take it they're not banned then? Even though most of them look like they'd happily munch on a child's arm like I'd eat a chicken wing.