Ok, a little geo-tirade:
the majority of minerals (especially the common ones) are salts of weak acids (carbonic, silicic) and strong bases (NaOH, KOH, Ca(OH)2) ie feldspars, pyroxenes, carbonates. Because of this character, they are typically stable under alkaline (ph greater than neutral) conditions, and tend to dissolve under acid conditions. The alkaline nature of these minerals will give most minerals (but not quartz) the ability to neutralize contaminant acidity. This neutralization can be relatively fast for carbonates (you could sit and watch it if you had enough beers, and it may be more entertaining than nascar) but is pretty slow for silicates (you will grow old and die watching)
On the flip side, certain minerals are the opposite: salts of strong acids and weak bases. they generally are the result of weathering of sulfide minerals like pyrite, marcasite and the like. In modern geologic settings at the earth's surface, these minerals are exposed by mining of ores, coal or in hydrothermal deposits. They can also exist as accessory minerals in shales . Acidity is produced when these minerals are dissolved in fresh (unsaturated) waters.
Now to add a little organic geochemistry: when organic materials (plants etc) break down one of the major steps along the decomposition pathway are humic and fulvic acids. these are huge molecules with a variety of structures. The importance of these is two fold: they have lots of removable H+ (acid producing sites); and they are a very common component of mud, especially stinky organic mud that we tend to see photos of trucks buried in on this forum.
Ok what does this have to do with clear coat? Well, my understanding of clearcoats (please correct me if I miss this) is that they are primarily urethane. urethane has some nice properties (can be clear, is somewhat flexible when set, relatively easy to work with) but it is poorly resistant to acid attack. it doesn't hold up at all in strong acids, and has limited service life in weak acids...it will form pits.
So depending on the geology of the specific hole you get stuck in, it can possibly be a pretty corrosive environment. that said, my 06 tacoma gets a new layer of mud or dust every day depending on the weather, and i don't have the time or inclination to wash it off every day. I guess that is why I bought the silver one.
:2cents: