OK I watched both the clips and the first thing that struck me is that both users have limited knowledge of their guns and are repeating something they heard without further research...maybe from the local gunshop commandos
1st clip: That is a 226 Navy, with the phosphated internals as a copy of the 226 supplied to the Navy SEALs. Neither the frame nor the magazine are coated in Nitron. The frame is hard anodized aluminum. The magazine is phosphate coated. A telling point is when he talks about the rust needing oil to remove...this would lead me to believe that he isn't properly maintaining his gun. If you have rust forming on your mags, you haven't cleaned them properly
2nd clip: This 226 isn't Nitron coated either. It is a folded carbon steel slide and Nitron was never the factory applied finish. I have some Sigs...notably a Israeli surplus 228 and another w/65k+ rounds used in competition...which have seen a lot of wear and don't look anything like that.
Two things come to mind and both are holster related.
1. improperly fitted holster
2. holster design which exposes the top of the slide to abrasion from the seat belt...I don't even think that would cause that much wear.
I've seen (50+) and purchased (4), or caused to be purchased (6), numerous LE trade-in Sigs and have never seen anything that bad...if I saw that kind of wear on a gun, I'd say it was abused