sst,
Since you are incapable to look up 2012 election results in yahoo or google. Here are the data from wiki and a few examples on why BO + MR equals not 100%:
Candidate Barry Mitt
Popular vote 65,387,995 60,724,672
Percentage 50.9% 47.3%
and by States from A to W:
Alaska
100% Reporting
Polls Close: (Nov. 6) 11 PM ET; (Nov. 7) 12 & 1 AM ET
State Results »
R Winner M. Romney 55.3% 136,848
D B. Obama (i) 41.3% 102,138
L G. Johnson 2.5% 6,131
G J. Stein 1.0% 2,366
Wyoming
100% Reporting
Polls Close: 9 PM ET
State Results »
R Winner M. Romney 69.3% 170,265
D B. Obama (i) 28.0% 68,780
L G. Johnson 2.2% 5,302
O V. Goode 0.6% 1,438