It was reported (I heard it from Navratilova from TC) that Safina and Kvitova were asked if they would switch to Armstrong due to the Roddick-Isner match being so long. Well, apparently that was not the case.
Safina said she wasn't asked. She was told by tournament officials. "They came to us at 9:10 p.m. and just told us to switch to Armstrong," she said. "Basically, that's it. It was very unfair. The best player in the world to put on Armstrong. Their answer was that they prefer a five-set match to a three-set woman match."
"That's it, they don't want to listen, just move to Armstrong," Safina said. "I keep asking why we're playing on Armstrong at 10. They tell us just play, go on, go on 10 on Armstrong."
"I'm No. 1 player in the world," she said. "Why move me? American Blake because they want five sets instead of three. I always look forward to play night session on Arthur Ashe, it's best thing in the U.S. Open."
Feel bad for Safina as she shouldn't have been ordered to do this. 
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Tournament officials did not want to delay the start of the Robredo-Blake match because the winner next faces Roger Federer, whose match finished before 2 p.m.
"You've got to balance safety issues, a big crowd -- but the No. 1 factor is competitive integrity," U.S. Open spokesman Chris Widmaier said. "If we had not split the matches, the women's match would have started at about 10:30, and who knows what time Blake and Robredo would have finished?"
Read more:
http://sportsillustrated.cnn.com/2009/tennis/09/06/safina.ousted.ap/index.html#ixzz0QOqrJESy-----
Tourney organizers can't win. They either move Safina, who's been playing rubbish matches, and get accused of US favoritism and disrespect, or they let Blake/Robredo play late and get accused of lacking integrity in terms of match scheduling. Given the options, I think they made the better choice.