Rio was the only choice for the IOC. London having the 2012 games paired with 2 of the last 5 Summer Olympics being in Europe (including Spain in 1992) pretty much pointed to Europe not getting another games. Same issue for Toyko. Bejing just hosted in 2008, so giving another games to Asia so soon probably had no chance. While the President's visit probably didn't help, the real killing blow to the Chicago bid was the Chicago Tribune poll back in the beginning of September that showed that nearly as many people in Chicago that didn't want the games as wanted them.
It wasn't the lesser of the evils, though. Rio does have a few things going for them. First, the fact that no South American city has ever hosted the Olympics I'm sure played a major part. Second, and probably the biggest point, the biggest day as far as viewership goes in any Olympic games is the opening ceremonies. With what Rio does every year on Fat Tuesday, can you imagine what the opening ceremonies are going to be like in 2016? This might be the first time the Olympic games come with a parental advisory label. After all of the accusations that have surrounded the Olympics for years, the IOC had to give it to Rio. The passion that the Brazilians will bring to the games will be one for the books.
As a resident of Wisconsin, am I sad that Chicago lost? A little. Yes, it would be cool to have such an international event so close. However, with the political corruption in Illinois and Wisconsin, we would have been screwed more by having the games than not having them.