Although not a pilot, I've spent lots of time on the flight deck during flight tests - and observed countless simulator sessions - and the PF has always had one hand on the throttles during approach/landing. I've assumed that was SOP and pilots who flew Boeings were taught to do that.
Several years ago I was involved training crews from an Asian military operator on the 737-Classic. I understood at the time the military wanted to expose their 737 crews to various training providers in Europe and USA rather than their own airlines. The first thing I picked up was that in flight both pilots had their hands firmly placed on their knees in between MCP selections during automatic flight.
Through the interpreter, I suggested that during any autopilot instrument approach it was wise to have one hand lightly on the throttles rather than both hands on the knees. My suggestion was curtly declined by the chief pilot who was PF and he continued with their own policy. Through the interpreter, I said that each throttle had a clutch motor and if a clutch motor happened to fail, the auto throttle would not move except by hand. By lightly resting one hand on the autothrottles during an approach, a split in the throttles could be quickly picked up.
Again this was ignored with an imperious wave of the chief pilot's hand. I found his attitude irritating especially as during the pre-flight briefing I specifically mentioned the wisdom of one hand resting lightly on the autothrottles during an instrument approach and particularly on final approach.
Accordingly, I re-positioned the simulator at 5000 ft on an automatic pilot/autothrottle descending DME arc leading into a coupled ILS approach. Both thrust levers were back at idle as expected for the clean descent at 210 knots. Via the instructor panel IOS, failure of the No.1 engine AT clutch motor was initiated while both throttles were at idle of 30% N1
Approaching 10 miles and coupled to the ILS, the pilot called for gear down, and various flap selections as the speed bled back at each flap selection until the automatic throttles started to increase thrust towards landing configuration thrust settings. Naturally, the No 1 thrust lever remained at idle as its clutch motor was inoperative. All the time both pilots had their hands on their knees apart from configuration selections by the co-pilot
At five miles in IMC on final, No. 2 engine was around 75%N1 to make up for the lack of thrust from the closed No.1 throttle which indicated 30% N1.. The autopilot was struggling to track the ILS under significant asymmetric power and the control wheel was now 45 degrees off centre. Rudders were central. Neither pilot said anything and did nothing but stolidly gaze at the displaced control wheel and presumably at the split in the thrust levers.
I was amazed, as I had never witnessed anything like this before. Eventually I leaned over to the interpreter who was sitting in the jump seat and asked her to tell the captain about the split in throttles with No.1 at idle and No.2 at 75%N1. Still with both hands on his knees the captain shouted at his co-pilot in Chinese that No.1 engine had failed and called for the engine failure and shut down checklist from the QRH. There was of course nothing wrong with the engine and the throttle could be moved manually if desired.
As the co-pilot dived to locate the QRH from somewhere on the cockpit floor (he never queried the captain's actions probably due to cultural mores), the autopilot disengaged itself under excessive control deflection, and the 737 started to roll rapidly left under the influence of asymmetric thrust. The captain still kept both of his hands on his knees making no attempt to stop the ever-increasing yaw and roll. He did however shout louder at the co-pilot presumably urging him to get to the right page of the QRH. I saw the co-pilot flipping the pages of the QRH as fast as a bank teller counting notes and I fully expected him to lick his fingers to get a faster flick.
I watched in great interest knowing that no one would ever believe my story at what I was seeing. By now the simulator ADI was showing 30 degrees nose down and 80 degrees angle of bank with a massive rate of descent. At no stage did the captain take his hands off his knees and at no stage did the co-pilot look up from flicking then pages of his QRH. All this below 1000 ft on final and in IMC.
All the captain had to do early in this drama was to use both throttles to get equal power and full aileron to level the wings and go-around. The GPWS was going mad and to avoid the inevitable loss of face that would have occurred with the chief pilot crashing the aircraft, I froze the simulator when the crash was inevitable.
We all went for coffee in silence. There was no point in labouring the point while culture reigned supreme. I didn't operate in the simulator with that crew again so I have no idea if they changed the company policy of hands on the knees on instrument approaches...