The Mezzanine

Sounds like the primary difference is in various concepts of 'sauce.'

I suppose ketchup is a 'sauce' but it's grouped in most people's minds as a condiment and sits besides yellow (or brown) mustard. Technically, a condiment can be a sauce as well, which I suppose ketchup is, but in this case I think it's closer to 'seasoning'. It tends to be a ingredient, not something used all on it's own or over something neutral like pasta.

It's not a particularly linear thing though because hot sauce is a condiment and not really a sauce so I'm not sure that there's much in the way of hard, fast rules about it. Still, I kind of understand why most Americans would make a face and say that ketchup isn't tomato sauce. Tomato sauce is something that's on pizza or spaghetti. Ketchup is kept in a bottle on tables in restaurants or in the refrigerator. So they tend to occupy different places in our heads.

Good and accurate point about marinara. I pretty much blame grocercy store marketing for labelling a whole section of the tomato sauces "marinara" with no explanation for it becoming an interchangeable substitute for a variety of tomato-based pasta sauces.