Whether flying ILS or PAPI or even visually to a runway without markings, the result is always the same - adjust the throttle to keep on the glide slope / approach.
This statement is not true. When flying the ILS at 100 kts, if you are above the glidslope you push forwards and if below, you pull back. Throttle then controls your speed...think of a 747 on a coupled approach with autothrottles maintaining a set speed. If the aeroplane is high, George (the AP) will push forward. If that results in higher airspeed then autothrottles will command less thrust.
Conversely, now imagine you are dragging yourself into a short strip under power. You have a high AoA and engine producing a lot of power. If you end up getting low, you increase throttle and bring you back up to the glide path (you don't pull back on the stick or you may stall). If you are high you reduce throttle and sink back onto the glide path.
Pace mentioned Energy Management, and that is what it is. This all depends on where you are on the drag curve which determines which control you should use for speed and height.