Track and Field is one of the marquee events for NBC along with swimming and gymnastics. Their goal is to show these events during prime time to capture the largest viewing audience. NBC had enough influence (money) to get swimming and gymnastics scheduled early in the day in Beijing so that they could be shown live on the East coast. They weren't able to influence the track schedule which is probably a good thing. Imagine the athletes having to run in the midday sun with that humidity. They could show it early in the day but they loose the appearance of showing a live event for the average viewer. I don't think it’s about favoring swimming over track it’s about showing both of these sports to the prime time audience.