This shouldn't surprise anyone:

The ambiguous season finale of “Grey’s Anatomy,” in which Dr. George O’Malley (played by T. R. Knight) and Dr. Isobel Stevens (Katherine Heigl) were left for dead — he, after being hit by a bus; she, after surgery for a brain tumor — earned Thursday’s largest television audience. According to Nielsen’s estimates, the episode, on ABC, was watched by 16.4 million viewers, the best showing for “Grey’s Anatomy” since its September premiere. ABC also averaged the most viewers for the night, and CBS came in second with “Survivor” (12 million), “CSI” (14.4 million) and “CSI: NY” (12.8 million). Fox was third with “Bones” (8.7 million) and “Hell’s Kitchen” (7.4 million). No one was killed on the finales of NBC’s shows “The Office” (6.8 million) and “30 Rock” (5.7 million), as the network placed fourth.

Suffering sells.