To do things like reflections and shadows using polygons you basicly have to code in special tricks to do it, but with raytracter those things come naturally. When games are starting to require reflections on reflections in pretty much any surface and advanced lighting, raytracing just might be faster, and the switch will be made.
Actually that won't happen. Direct X 10.1 addresses the fact that you have many reflections using techniques such as cubemap arrays and independent blending modes. So, again we won't need raytrace to do these things anymore. Already you can do pretty nice shadows without raytrace (Doom 3 is still a good example, but how about Crysis?). Yes of course, call them tricks all you want, they still play fine in realtime and they run on actual hardware that requires less than a mainframe in electrical charge.