I heard somewhere it's got something to do with the early cable machines being set up that way because the engines turned one direction and all the mechanicals were thus on the left hand side to keep the drums turning the same direction. Early hydraulic machines were sort of a hybrid mechanical drive/hydraulic, for instance my old Bantam C450 had friction swing and track drive but the work group was all hydraulic. It had all the clutches for the drive on the left hand side of the machine, yet you shared the cab with the reduction drive chain box on the right side of the machine, but I would imagine they could have put it on what ever side they wanted as the mechanical drive all came from a hydraulic motor anyway. I would imagine all the old line american manufacturers left the cab on the right hand side because that's the way it had been done but then they migrated to the left for some reason or another... Now if only we could all agree on one control pattern.......... Even Caterpillar's excavator prototype (I think it was called the 625X-1) had the cab on the right hand side...