So Campy chains used to be 6.2mm wide, then (without changing sprockets or anything else) they moved to 5.9mm.
Used to be 6.1mm. That's right, they moved to a narrower chain without changing anything else. "Noise" was mentioned in the catalogues, so I believe that was the reason for it. I suppose they are also a tiny bit lighter.
Some Campy-compatible chains are (were?) still 6.2mm.
Yep, they don't seem to have caught on that Campag have narrowed their chains, so they are behind the times.
What width are Shimano chains?
Can't remember exactly, but narrower than 6.1mm. I would think about using them with my Campag 10-speed systems if they were
much cheaper. Meanwhile I'll stick with the devil I know. Campag chains are very well made.