Yes of course they go down, it's just a question of where.
By keeping the vertical part of plumbing out from under your toilet and bathroom in general, you get different options for designing your building.
By keeping your plumbing runs in a wall chase you can access them without a sledge or jackhammer.
At work I am often entering large utility chases, and even though the space is tight, its much better than the crawlspaces I've been in.
They are usually multistory, with expanded metal flooring on each level.
I can imagine a central utility room acting as a big walk in chase, with laundry, bathing , toilet and kitchen clustered around it, in single family house.
Add your furnace and electrical panel , land line and Internet and basically you have an above ground basement, so what's the point?
Well basements are expensive, that's the point.
What if instead of the adding the other utilities to the first floor utility room, we add stairs to a utility attic?
Only the plumbing needs to be run through the foundation, everything else can probably go upstairs.
This mimics some of the commercial buildings I'm familiar with, with most of their HVAC equipment in their penthouse instead of in a basement.