I don't think it is, though I think it is used for sport over there because it handles motion better. I think ABC and Fox are 720p, which probably has something to do with them showing a fair amount of sport.
In some European countries, like Germany, 720p is the standard though.
The reality is that the 720p benefit over 1080i isn't huge in motion terms, and the increased horizontal resolution of 1080i, particularly relevant on drama and movies, is proving a bigger force.
The unspoken issue is that most broadcasters who are broadcasting in 720p are doing so just at the final stages of transmission, with 1080i dominant in studio and production still (along with 1080p for episodic drama, movies and some docs)
In Europe lots of the 720p broadcasters still run their studios and OB trucks 1080i and cross-convert to 720p for transmission. The argument is that a broadcast quality deinterlace is better than a domestic one, but there is also an argument that 720p can be compressed more... (I think NRK even run their pres areas in 1080i and downconvert to 720p after playout)
Even though Fox and ABC/ESPN run 720p for broadcast (and in some cases they originate in 720p) - almost every single major large international sporting event is host broadcast 1080i. The Olympics, the FIFA World Cup, The Rugby World Cup etc.
The Eurovision Song contest has been hosted by SVT, DR, NRK and ARD(ish) over the last few years. All of them are 720p broadcasters. But the show has been originated in 1080i not 720p every year.