It's obvious you haven't seen a FOX NFL broadcast then, because CBS's 1080i blows away FOX's 720p broadcasts any day of the week!
So does NBC's, but I submit the differences are more related to other factors than to the differences between those formats. Other factors include: camera quality. Skill in camera use and placement. Initial compression. Transmission quality. Secondary or tertiary compression. Quality of TV monitor, esp. its ability to display each format.