Baseball and softball can apply for readmission for the 2016 Olympics. But I suppose the allure of watching AA and AAA players duke it out against Cuba for the gold medal didn't appeal to a lot of people. IOC member Anita DeFrantz appealed for softball's reinstatement separate from baseball, but did not get enough support to even bring the matter to a vote.
The 2012 Olympics will have 26 different sports on its schedule. The IOC limits the number of sports to 28. Other sports that have also tried to get included, but failed are: karate, rugby sevens, and roller skating.
UpdateThis story from the AP has more detail on the vote and quotes from the principals.
This part was interesting to me - During a debate before the vote, more than a dozen members but only one European spoke in favor of bringing the two sports back. Notably, the only one who spoke out against was a prominent European Crown Prince Willem Alexander of the Netherlands.
For that injustice, we're not going to let the Dutch team have Andruw Jones for the WBC. Or Mark Mulder. Or Shea Hillenbrand.