Not sure where you fly but around here, ARO is used far more often than not. Very common anong the aircraft modelers here. I generally avoid the boat and car folks so can't speak for them.
I however did not suggest what you were seeing is not rust, just that I prefer to see a bit of varnish over the typical rust issues.
Two rules, 1. Don't sweat the small stuff, 2. It's all small stuff.