According to a July, 2009, NPR story, a British Columbia Supreme Court justice ruled that allowing a men's ski jump event but not a women's constitutes discrimination. Unfortunately, the Canadian courts don't make the decisions about Olympic events, the International Olympic Committee (IOC) does.
The IOC claims that gender has nothing to do with their decision not to include women's ski jump. They state that it's entirely technical. The NPR article says:
Those technical issues include the number of women ski jumping at an elite level and the number of countries competing in the sport. IOC officials have argued that too few women and countries compete to justify Olympic competition.
Apparently there aren't that many male ski jumpers either, but the sport is always included because of tradition (it is one of the oldest Winter Game sports).
Ironically, prior to the 2010 games, the world record holder for the ski jump was a woman! She's an American named Lindsey Van, and beat the record for any woman OR man. She even achieved that record on the exact same hill in Vancouver that the ski jump events are held on this year.
Olympians are still going to fight for the women's ski jump in the 2014 games, but we'll have to just wait and see.