I think we should differenciate between suburban and rural dogs. Suburban dogs are used to pedestrian traffic and neighbors. Rural dogs may think they live under the only porch there is and have never seen anyone walking other than their owners, and only very rarely ever see a bicycle (you may be the first).

When the rural dog takes off after a bike the dog may not be engaging in a recreational activity. He may think he's defending his pack from a dangerous predator, defending his territory, wondering if you would be good to eat, or chasing off a DEA officer. Or he may be a well socialized dog that's just giving a playful chase while the owner isn't looking.

The suburban dog is a much lower risk to the cyclist.