Can go both ways depending on climate. If freezing isn't an issue the pipe exit the slab in one spot and go through the attic. If freezing is an issue its common for the pipes to be buried through out the home and rarely through the walls anymore.
Not on the West Coast of Florida.
About the only place we water pipe overhead is in condos and apartment buildings.
In single family homes we never pipe in the attic. We water pipe under the slab and jumpup into the walls with a manifold to branch out to other fixtures.
There are several reasons for this;
1) The expense! It takes more time and material to pipe overhead.
2) It's a safety thing. If you should develop a leak where would you rather it leaked into. The dirt under the slab or raining down from the attic onto your furniture annd carpet?
Regards, Tom