Neat stuff. It's worth noting that shadow rays don't entirely avoid precision issues either. You still need to handle self-intersections. One option is to add a bias epsilon (which introduces other artifacts, depending on the scale); another is to reject local self-shadowing (which means you can't get finely shadowed surface cracks); another is to give artists explicit control over which sets of objects shadow which others (which adds artist time). Offline rendered movies use all of these.
Generally speaking, the biases needed for ray-tracing are much smaller than the biases needed for shadow mapping. Ray-tracing tests directly against the geometry so only needs a bias proportional to the numerical accuracy used, whereas shadow mapping requires bias proportional to the texel resolution of the map.
While these are all potential solutions that also are the same as in shadow buffers, you have the additional ability to play tricks such as, skipping intersection with the casting triangle, and similar tricks that solve the problem much more completely, if at a performance cost.
