I think that with knowledgable distance announcers people would like to see distance races (5 and 10). The majority of the people watching these can identify with a distance race much better than they can a sprint race. How many people in the U.S. run 5k's,10k's and marathons every year? Then think about how many run 100's, 200's, 400's etc.People know a little about the distances because they do it but they can't identify with sprinters.