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I'd like to learn more about the grounding here.

We have sandy soil that is very acidic. Typical pH around 4 or so, up to 6.

E3608.1.4Rod and pipe electrodes.

Rod and pipe electrodes not less than 8 feet (2438 mm) in length and consisting of the following materials shall be considered as a grounding electrode:

• 1.Grounding electrodes of pipe or conduit shall not be smaller than trade size ³/₄ (metric designator 21) and, where of iron or steel, shall have the outer surface galvanized or otherwise metal-coated for corrosion protection.
• 2.Rod-type grounding electrodes of stainless steel and copper or zinc-coated steel shall be at least ⁵/₈ inch (15.9 mm) in diameter unless listed. [250.52(A)(5)]

E3608.1.4.1 Installation.

The rod and pipe electrodes shall be installed such that at least 8 feet (2438 mm) of length is in contact with the soil. They shall be driven to a depth of not less than 8 feet (2438 mm) except that, where rock bottom is encountered, electrodes shall be driven at an oblique angle not to exceed 45 degrees (0.79 rad) from the vertical or shall be buried in a trench that is at least 30 inches (762 mm) deep. The upper end of the electrodes shall be flush with or below ground level except where the aboveground end and the grounding electrode conductor attachment are protected against physical damage. (250.53(G)]

Curious why they wouldn't use copper ? 

Probably cost?  Copper is  expensive.  That's why thieves are still stealing copper wire from poorly guarded new construction sites and other places.

I see now that they do list copper on that spec.  They use a special jackhammer here to get the copper down 8 feet.  I see they call this Galvan, which I assume is some kind of copper alloy.  Didn't realize that.