Just to throw another comment into the mix...

A friend of mine has a 2000 Blazer and it is loaded (every option). One thing that it has under the hood is a few circuits that run from the battery to the chassis/frame and various body panels and emits a constant small trickle charge through those parts. This was installed at the factory and is supposed to "inhibit corrosion".

Check with some GM dealers/assembly plants, maybe they can shed more light on this.