I read an article about this a few years ago that mentioned that it sorta works off the concept of resonating frequency, but they must limit the range because once the power goes a certain distance, anything that picks it up interprets it as power. i.e. 120 volts broadcast over, say 30 feet will electrocute anyone in that vicinity. But if you are closer it passes through you, harmless.
Why not make this on a much more localized scale, like inches or a fraction of an inch? I have an electric toothbrush that does this. I've long wished my phone had a similar simple cradle (ahem, maybe even standardized!) that I could set it in and charge it wirelessly. Yes I know there are cradles now, but they require actually plugging into a fixed connector. I think I saw an add-on for iPhones once that did this.