Factors, body types....
Rust or wear can be different for different people due to a # of factors or reasons.
Body temperature, Ph balance in your sweat or humidity, rain, fog, smoke, dust, sea-spray, etc.
In the early 1990s, I had a strange patch where I somehow coded out 3 different bank cards(ATM) in a span of about 3 weeks.
I wasn't near any huge computers or machines and kept each card in my nylon wallet. This was before cell phones & PDAs too.
Blue or black handguns can be kept rust free or have reduced corrosion but you'd need to wipe it off with a well made CLP like Ballistol or FrogLube or Eezox everyday.
Poorly made holsters or leather can damage handguns too. Grit, crud or moisture can collect on the frame or slide.
While in the US Army in Panama, I saw a plain clothes MP investigator draw & clear a M9 Beretta 9mm. He had a cheap belt slide type holster & the M9 had brown rust spots all over it from the leather rig. I doubt the MPI was ever oiling or using any Breakfree on it.
As noted, if you want extra protection or constantly work in a marine environment, Id highly suggest a good surface treatment like NP3+, Metalife,, Bearcoat or Cerakote.