I've never heard of 120 cd/m2 being the "conventional wisdom".
Most people I believe set the screen brightness to match the print, and on my monitor that's 105 cd/m2.
Yes, it makes sense to load a different profile for images that will be viewed on another medium. But for the general public wouldn't that be a bit hit-and-miss? Monitors, smart phones, tablets, televisions etc.
David