Correct me if I'm wrong, but early on in the HD evolutionary process, 720p was deemed to be better for sports due to the fact that it was 720p/60, while, as previously stated, 1080i/60 is effectively 1080p/30. Seeing a hockey puck move in 60fps vs. 30fps provided clearer tracking. That is why Fox/ESPN broadcast in 720p.
Also, as stated above, it is likely that any 1080p broadcasts are likely 1080p/30 due to the bandwidth required to broadcast 1080p/60, but they'll never tell you how many fps they're broadcasting in!
FYI. Here is a very helpful link to a chart that gives distances and screen sizes for viewing the different HD resolutions. It is based on the ability of the human eye to see detail:
http://hdguru.com/hdtv-seating-distance-chart/6/ Basically, it tells me that I need to be sitting 7 feet from my 55" SXRD to see a difference between 1080p and 720p.