The somewhat simplified "pitch = airspeed, power = climb/descent rate"-idea might not appeal to you, but IMHO there are two good reasons for teaching it (besides the fact that it is largely correct).
First, in the usual low-performance PPL-training airplane, pitch has a more immediate effect on airspeed than power, so if you need speed quickly, pitching down will produce the desired result faster than adding power.
Secondly (and relatedly), it's a safety net. If you ever get too slow ("mushing regime" or "back side of the power curve", in case you want to search for more detailed explanations) on one of your first solo approaches (which is of course a purely theoretical assumption for an outstanding top gun in the making ;-)) and get too low, instinctively adding power to gain airspeed and pulling back on the yoke/stick to arrest the descent can turn out so bad as to produce a power-on stall and probably even a spin in adverse circumstances, almost certainly resulting in the loss of a low-performance airplane and a high-potential student. If you acquire the habit of countering a too-low airspeed by lowering the nose first and adding power later (and that is something you need to consciously train), you unload the wing and get out of the mushing regime, greatly reducing the risk of terminally damaging yourself and the airplane.
Last edited by Armchairflyer; 8th May 2012 at 15:45.
Reason: Edit: Sorry for repeating explanations already made in recent previous posts.