Primarily to nex. Speaking as someone who has produced quite a few printer drivers for RISC OS users I can tell exactly why they are not generally free. The printers, paper and ink needed to produce the drivers are not free!!! I have to buy all the above items to be able to produce drivers. If I didn't buy them AND my users didn't make donations in return there would be no drivers from me.
Once the driver is released I then generally sell the printer, but of course I never get more than I paid for it so someone HAS to pay.
Dealers selling printers may be able to get away without paying for a printer to develop on but they certainly still have to pay for ink and paper consumed.