It is amazing how myths never die. A receiver is a tuner, preamp, and power amp (and these days, typically also a processor) all in one box. With separates, these things are in separate boxes. Counting boxes is no way to determine quality.
Also, extra power is only useful if actually used. If you have speakers that are difficult to drive (e.g., low impedance, inefficient), or you listen at literally deafening levels of sound, then lots of power may be called for, but otherwise, any difference heard with typical equipment will be a result of lack of level matching and the placebo effect (i.e., in the person's head, not real). If you doubt this, do some double blind listening with level matched equipment with speakers that do not require lots of power.