Roper says that the more removed a setting is from real life, the more difficult it is to focus on a great storyline. If you, however, set Spiderman swinging from the skyscrapers of New York, citizens of that city can identify with him because they have walked those very same streets. Another major factor in the trend toward sci-fi gaming is the stranglehold World of Warcraft has on the fantasy genre. Blizzard is king when it comes to fantasy gaming, and the more titles that come up against it prove that WoW is too entrenched to be moved. It is simply more cost effective to make a sci-fi game these days, in the face of a MMO giant that works within the genre so well.
Personally, I wonder if the trend toward sci-fi games and movies represents a shift from a literate society to an alliterate one. In previous years fantasy novels were incredibly popular, much more so than their sci-fi cousins. But the less we read as a culture, the more we look to be entertained through experience, through dynamic movement, through engaging our future today instead of waiting until it actually arrives. I see this as a major reason why we prefer to race flying cars than classic ones, why our guns are laser rifles rather than six-shooters, and why the protagonist's ears are no longer pointed.