I'm in the UK and would say it is the norm here - certainly if you buy a pre-packaged sandwich it would have butter (well, usually margarine) .
My sister's in-laws don't - my BiL's parents are both old enough to have grown up during the war and have always operated on a 'butter OR jam' basis (which when fat was very strictly rationed would make sense) and they have never broken the habit.
We think my BiL is slightly odd for *not* having any butter on his toast-and-marmalade, he thinks we're slightly odd for having both.
I personally don't always use butter - it depends what kind of sandwich I'm making (I don't bother f I'm having something gloopy like jam or peanut butter.) but I would see it as a standard part of making a sandwich.
(PS - I don't want your tomaot sauce sandwich, - my favourite is fresh, crusty white bread, real butter, cold roast beef, tomato and little bit of wholegrain mustanrd. Pure bliss)