WASHINGTON - About 21 million people will begin receiving benefits through Medicare's prescription drug program in January, officials said Thursday, a figure that exceeded the government's expectations but only includes about 1 million who voluntarily chose to enroll. The rest were either enrolled automatically by the government, or they will receive benefits through their private health care plans. Medicare opened enrollment in the program on Nov. 15; it ends May 15. Health and Human Services Secretary Mike Leavitt told reporters that the government expects to sign up between 28 and 30 million people for the benefit during its first year....