Well fact is some people do care about noise while playing. Think that for example in Crysis you are alone most of the time and birds choring is as much as you hear, but the card would be almost 100% loaded. It is annoying.
I do care about the sound myself while I'm playing, but I don't think that ANY card will ever be louder than my power supply anyway. I have never used one of those cards that do 50+ db on the reviews though, I usually choose the silent ones. Every card is silent in comparison to my power supply, it
was silent but not anymore, I bent it's fan a bit while cleaning it from dust sadly. That's why I use headphones instead of my 5.1 setup most of the times until I replace it. But don't think the PS does a lot of noise. It's just that I paid a lot to have a noise free (clean sound) sound setup just to let something spoil it.
Ey! You got the idea!