Attitude+Performance=Performance
I was taught to pitch for airspeed myself, but have later found that that shouldnt be done (unless your doing carrier landings. Aerodynamics for Naval Aviators mentions this)
When flying light trainer aircrafts pitching or adjusting power for altitude wont really make a big difference since the airspeed is very slow.
But consider:
1 degree of pitch change equals a change in vertical speed of aprox. 2% of the airspeed. Since 1 knot is aprox 100 FPM (feet per minute) you can see that 2% of 100knots=200 FPM, 2% of 250 knots=500 FPM. This relationship holds true in any airplane as long as the speed is held constant and is accurate to about 10%.
So you can see from this that pitching for airspeed or altitude doesnt matter much in a C172 with approachspeed around 80-90 knots, but its quite significant when your flying heavy aircrafts approaching at 15-180knots, or flying enroute at several hundred knots.