What am I missing on this line. (Olympic Women's swimming)

[zootiehead]

Swimming - Women's 4x100m Medley Relay - winner
Sat 8/16 303 USA wins Women's 4x100m Medley Relay +250
10:40PM (EST) 304 Field wins Women's 4x100m Medley -300
Sat 8/16 305 AUS wins Women's 4x100m Medley Relay -320
10:40PM (EST) 306 Field wins Women's 4x100m Medley +260

Why would anyone take US +250 to win when they could get them +260 plus the rest of the field to win over AUS?