Yes.
I think more than "a very tiny amount" of 3DS systems are contained within a household where there's more than one person who owns a 3DS. Each one of those gets up to three passes each day. One family that comes to my StreetPass meet-ups consists of a mother, father and three kids who all have a 3DS.
Kids and college students who go to classes with people could easily get a pass from the same person every school day. There's 180-ish passes there.
I work with two people who carry their 3DS to work most every day and I'm sure many adults do carry their 3DS to work (and in the case of those in larger cities, on some form of Mass Transit).
I seriously think you are underestimating the amount of clustered 3DS systems.
But, as I said earlier, I'll just state that I disagree with your assertion.