bridged mode vs stereo

i see that some poweramp have better damping factor and s/n ratio when they are in bridged mode vs stereo. I would like to know if its a universal laws?
No. Give us an example.
I tried a few in the past mostly out of curiosity, and always found the amp to sound better in its stereo mode. Don't forget, everything will be going through roughly twice the gain/signal parts wired this way. Doesn't make sense to me. Also a 4 ohm (lowest impedance) rated amp can only handle 8 ohm loads wired this way, with the ones I tried.