I guess every soldering gun is 50/60Hz. However I was thinking that the sk in effect is very dramatic with iron and the impedance will increase rapidl y with frequency. It seems like a way to concentrate more of the power into the tip of the iron rather than having a lot of power being dissipated in the windings/connections etc. You would have to be careful about what would happen at the curie point of the iron tip if it should ever get (red) hot.
I found this curiosity as well: