Aggressive dogs have always seemed more like a suburban/rural problem to me. Growing up in a suburb I had dogs ignoring their electric (or nonexistent) fences to bark and chase me on pretty much every run. The leashed dogs also sucked and a decent percent of the ones I passed would snarl and lunge at me. I dont know of anyone who actually got injured by a dog on a run, but there were definitely some scary experiences.
On the other hand, over the past 11 years of living in cities I cant think of a single time I've felt threatened by a dog. I pass maybe a dozen dogs per day, many off leash, while running in the park and they more or less ignore runners. I can only think of two times I was chased by dogs, and they were both escaped puppies that weren't even a little threatening.
I think the issue is that negligent suburban dog owners leave their dogs outside all day, where they become defensive of their territory and agressive, while negligent coty dog owners just never take them outside.