Michael,
When they built my house (November 2002 through February 2003), they did the same thing... just tossed any wires that went along the trusses up there without anything securing them.
Technically in Iowa, you only need to secure the romex at the outlet box or if it is exposed from the living space side.
They also used metal staples (no insulation) just as they did for you.
I'm glad to see progress on your studio!! Looks cool... I took the WHOLE week off last week to do some drywalling on the house... and I got ONE piece up before I ran into an issue... and of course the issue required contractors who won't come out until sometime THIS week... I got *NOTHING* accomplished.
Velvet Elvis