Originally Posted by joecaption
And would be a whole lot more work.
Agreed. But it's been the standard way of doing it here for years for cheap, mass-produced stairs. One advantage is that it enables the stairs to be strong and rigid, yet built out of cheap, thin material.
Typically, treads can be 7/8" pine (or even less if plywood) and risers can be 3/8" plywood or mdf.
My own home is 90 years old and the staircase treads are 1"piranah pine, tongued with 3/4" risers, and 1 1/4" thick strings and they're fine, with only one tread which squeaks, (but that just adds to the character).