Does anyone know if Pixologic charges a transfer fee if a PC license is transfered to a new owner who is on a Mac?
A license cannot be transferred to someone on a different platform. The only option to change platforms is to purchase a second license, which is provided at a 50% discount. If you were to do that, you could transfer both the PC and Mac licenses together, but you would not be able to break them up.
There are technical reasons behind this.