We don't have a fenced-in yard either, and going for a walk is such a joyful time for our greys. They look around and sniff and also learn to approach others (dog and human) with curiosity and respect. It is a wonderful bonding time for us with them as well.
I agree with Susan that dogs without fenced yards probably get more exercise than those whose homes have a fenced yard. A tired greyhound is a good greyhound! It also provides excellent daily exercise for the humans.