But in a transformer the coils are very close to each other, and are wrapped around the same lump of iron. With the devices the coils and cores are separate. Magnetic fields decay exponentially so even a small gap will reduce the transmitted power by a fair bit. There seems to be various proposed methods to get around this problem, but none of them seem to be significantly better than the others.

Interesting point about electronics reducing the idle currents, as this would be another issue.