When did nis 2010 start going quiet when full screen video?

Hi

Ive been away from nis 2010 for a month (I tried a comcast free 360 version but Im back to nis)

Im curious when nis started turning itself to quiet or silent mode by itself when I run full screen video online?

 

Am I nuts, or isnt it doing this automatically?

 

Its a nice feature I just wondered if it was doing it ever since I loaded 2010 and Id not noticed it.  I cant recall how long Ive actually had 2010 I upgraded to it from 09 a few months back.

 

Thanks for humoring me :) just wondered since my power of observations lack much!