The Roomba stuff does use IR for homing in. In fact, if you browse the inventor portion of their site, I remember seeing a white paper on it (look at their white papers for the Create platform).
Inductive charging would be bad for robots I think, as it would cause all sorts of RF at the microprocessor level. I have some of those candles that charge inductively, and they not only take forever to charge, but also require three foot clearance from other electronics (or so the manual says).
--- Edit ---
Ok, slightly mispoke. There are far less details then I remembered.
On page 18 of the Create Open Interface
it shows that the iRobot base station emits three fields of IR, based on distance, and offset location.
If we were to do this homebrew, I imagine we could do the same thing, with multiple frequencies of IR encoding.