I think a possibility is that some of the people that don’t see the difference have their monitors adjusted with a higher blackpoint, so don’t see the noise differences. I have mine calibrated to I can see all the black levels.
It’s probably also a style preference for flat, noiseless backgrounds. To me, it’s a pet-peeve and it destroys my perception of 3d space. To each their own on that one.
I like process my pics such that noise is apparent at 2x, still visible at about 1.5x and just visible at 1x. Just my preference.
Astrobin is a bit of a quandry, though, since each persons 100% magnification is dependent on their own windows scaling, so it’s probably 125-150% or more depending on that windows setting if you compare 1x in photoshop with astrobin.