During a pre-drywall inspection, one thing very important to look for are sturdy, metal plates covering any electrical or plumbing installation that could possibly be hit by a nail. The last thing you would want is to hang that beautiful painting and have sparks or water spewing from the wall when your nail punctures something you did not know was there!
Imagining what it would be like to do that with a gas line kind of sticks in my craw (if I had a craw that is...).
One thing we can't have enough of in life is peg board. You might not think that is true, but, of course, it is a simple fact of life.
Imagine this, or some future home owner, deciding that he needed his peg board to wrap around that corner of his garage. He gets out the trusty stud finder and determines that there are horizontal studs right where he needs them!
The peg board is going to hold heavy tools so it has to be installed with some strength! And he gets out the 2x4s and nails them to the wall! A 2x4 requires a pretty good nail, so those 16Ds ought to work really well! A 16D, also called 16 penny nail, is 3.5" long! Using enough force, would anyone be strong enough to puncture this black iron gas pipe? I would not want to find out.
I pictured that as I entered this garage! The County has already approved this house. You mean to say that vulnerable electrical and plumbing locations need protection, but not a gas line?
And I do understand that the 2006 International Residency Code for gas pipe installation does not "require" a protective plate (defined as 1/16th" or 1.6mm thick steel) to cover this notched location, but really, why not put one anyway? Garages are places where people nail and screw stuff to the walls! The code is not intended to be confining! It is the floor from which standards derive, and becomes the minimal standard.
My recommendation: when you see something that looks marginal, bring it up! This homeowner will remember that this gas pipe is there, but a future homeowner would have no idea.