power supply - What's the need for higher frequency in inductive charging systems?

Consider an inductive charging system like Magne Charge - it has a rather huge "coupler" coil off the vehicle and a corresponding slot on the vehicle and the coils in the "coupler" and in the slot are aligned perfectly parallel and brought close to each other. So it looks like a good old transformer.

Yet there's a huge box in each Magne Charge system (a wall-mounted unit) that most likely generates higher frequency current. Btw this box seems to be accountable for huge energy losses.

What's the need for that frequency increase? A good old transformer will run at the same frequency as mains - 50 or 60 Hz depending on the region - and have pretty good efficiency. Why would this slightly altered transformer setup need higher frequency?

Answer

It all boils down to efficency.

As the frequency a transformer runs at increases, the transformer can be physically smaller.

To Plagiarize Quote Wikipedia:

The EMF of a transformer at a given flux density increases with frequency. By operating at higher frequencies, transformers can be physically more compact because a given core is able to transfer more power without reaching saturation and fewer turns are needed to achieve the same impedance.

Consider the size required for a 50/60 Hz transformer capable of 6.6 - 50 KW (the power rating range of the Magne-Charge systems).