You missed the first part of that phrase where I said "seeing too much of someone". If their pants can't stay up far enough to keep from seeing their ass (whether their pants are snug, or they're wearing suspenders or some other means of keeping their pants up), then by most standards it is indecent for them to not wear a belt (or tighter pants, suspenders, etc).
I see a lot of fairly well dressed farmers wearing suspenders. Must be an region thing.