I concur with everything everyone has said!
I am quite familiar with England and have spent a great deal of time there. In my opinion, people there are far more "dog" friendly than they are in North America. Since I am Canadian, I can't really speak for the US, but I'm not surprised to hear that people tend to keep to themselves.
I agree with you Charles. It IS rude! It takes no amount of time to say hello, and even something as banal as "my dog doesn't do well with other dogs, excuse me". I think Jayme had a great suggestion about continuing to say hello, wave and smile. I often kill people with kindness, and generally make friends wherever I go, whether they like it or not.
Some people are just rude! If you are a stranger, then they don't wish to know. It is quite sad really. The world would be a much nicer place if everyone stopped being so wary of everyone else and actually took the 2 seconds to smile and say hello.
Vanessa, I would continue to smile and wave too!