Christopher Evans of Crytek, the maker of the Crysis series of games, gave a wonderful talk about film-game convergence at SIGGRAPH 2012. Video games and motion pictures share have many common processes: 3D modeling, visual effects, and physical simulation are used heavily in both mediums. It is in a way surprising that a lot of the infrastructure isn't shared between the two.
There are some major differences between the two which can explain some of the divergence. Film tends to be linear, static, and two-dimensional. There is time to hand-craft every last detail of a scene, and to perfect the physics of every last shard of glass that is projected towards the viewers. There's lots of place for direction and auteurism.
On the other hand, video games are all about non-linearity, dynamism, and 3D. Framerates have to be kept interactive (usually meaning >30/second) so that a game feels smooth, meaning that everything is optimized for speed. Although complex simulations and events are possible, it's often difficult to get exactly the desired look and feel for a sequence of actions.
However, more and more directors are beginning to see the potential of video game engines, such as Crytek's own CryENGINE. The realtime interactivity provided by video games allows for quick "pre-vis", a kind of puppet version of a scene that allows directors to preview how things will roughly look, without having to assemble a crew and a set. Indeed, Chris pointed out some case studies, such as the movie A.I., which used Unreal engine to scout locations before shooting actual scenes.
-- CryEngine 3
Today, many tools for cinematic rendering using video game engines are under development. Crytek's Cinebox adds critical film functionality including camera settings, motion capture, and pipeline integration to CryENGINE. Other tools, such as Source Filmmaker, make it easy to reuse video game assets like character models in custom movie clips. Some video games, like EA's Skate, have even added basic in-game video editing capabilities to allow players to make simple cinematics from their gameplay.
It will be exciting to see what the future holds for these fields together. Whether in the form of more cinematic games or more interactive movies, it's almost inevitable that the lines will begin to blur more and more as realtime rendering techniques continue to advance.