Great article by Annalee Newitz of io9.com about FlashFoward:

One rationale is pure economics: you dont have to make the future world. But its also about audience. For example, heres the difference between Battlestar Galactica and Lost. Lost gets 10 million viewers and Battlestar Galactica rarely tops 1 million, even if Battlestar Galactica is arguably a better show. And thats because as soon as audience sees robots and aliens, it dries up. They tune into other channels. Not showing the future on FastForward allows the audience to build.

READ THE REST @ i09