This might be hardly as surprise as Serena had a wonderful season to have a smashing 68-5 win/loss, record win 9 tournaments and 2 slams (Roland Garros and US Open).
This will be the 3rd year that Serena will end at the top of the rankings after 2002 and 2009.
From the WTA
Stacey Allaster, WTA Chairman and CEO, commented “Serena has proven time and time again throughout her career that she is an incredible champion, both on and off the court. This season she continues to rewrite the record books, proving she is one of the sport’s greatest athletes of all time.”