There are two huge factors, the first even more potent than the second. First, there is much more information per sample and per pixel. Normals, depth, separat

There are two huge factors, the first even more potent than the second. First, there is much more information per sample and per pixel. Normals, depth, separate diffuse color, separate diffuse texture, first bounce normal, first bounce position, etc. There is a technique that just uses color, but uses histograms of all the samples within a pixel. Second, for a video game you can accumulate samples temporally. Many of these demos will use one sample per pixel, but filtering information can be kept on every frame and reused to some degree.