Felix and Richards probably would have liked to try the 200 and 400 double if the schedule were different.
Article after last year's world championships where Felix beat Richards:
http://www.washingtonpost.com/wp-dyn/content/article/2007/08/31/AR2007083102172_pf.html
The victory in hand, Felix turned the tables and said she was considering turning her attention more fully to the 400, Richards's specialty, upping the ante on their growing rivalry and raising the possibility that both she and Richards would chase a 200-400 double at the 2008 Summer Games.
Philip Hersh's blog
http://latimesblogs.latimes.com/olympics_blog/2008/07/richards-felix.html
The international track federation deprived the world of a possible Beijing showdown between the two U.S. stars by refusing to make a schedule change that would have made a 200/400 double practicable in the Olympics.
That left Felix to concentrate on the 200 and Richards the 400, the races that each won handily at the U.S. trials in Eugene.