For 75-85 dB a few watts are enough so ...

Because we're trying to reproduce music, not just sound.

This is an bizarre concept to most of us, but work is the function of energy over time and when there is little time to do a lot of work, it takes a lot of energy.

"Because we're trying to reproduce music, not just sound"

Let me fix it for you:

We are trying to reproduce a stereo mix which boils down to multi channels such as guitar, vocals, drums, bass, keyboard, mic's that pic up room echo, etc. being processed into left and right. Then we obsess about how to fix things when the "images" are bunched up due to:
underpowered (chose your class and topology) amp, poor cables, poor transducer dispersion, lowly preamps, fill in the blank...

The concept of imaging w.r.t. the stereo mix is met with skepticism in my mind...sure I like "holographic" sound but it's all an illusion.

I also believe that this subject can be rather misleading to some. Sound pressure operates in a logarithmic scale. The difference between 1 and 10 watts is perceived as a 3db increase or a doubling of the volume. 10 to 100, then 100 to a 1000. So 500 watts is not "that" much more than 100. You cannot just say 500 watts is 5x more than 100. What it does allow is more current output and a better handling of steep impedance curves.

Thank all your for your responses! I got it know! Macd made a good point: it has to do with the logaritmic scale. Doubling the power does not mean to doble the perceived sound presurre level just a 3 Db increse. Thanks again.

You also have to keep in mind that a low powered amp pushing a hard load can clip because of the lack of head room. You may not even know your destroying the speaker beacause of soft clipping.