It totally applies there @kijanki - imagine 10 nV on the IC and then amplifying that small, medium or large.
Then you're talking about noise pickup by interconnect. That was mentioned as second reason. First reason was that amp with fixed gain and signal divider at the input will react the same way to electrical noise pickup inside of the amplifier at all positions of the input divider, while amplifier with lower overall gain will be less susceptible to electrical noise pickup inside of the box.