koraks said:

In fact, contams are a matter of concern in the wild. Or, to put it differently: the shroom mycelium itself is a contam seen from the viewpoint of other fungi. To put it differently yet again: fungi battle for supremecy in a habitat. Sometimes, the shroom mycelium will win, sometimes some other mushroom will come out on top, sometimes only molds manage to get a good hold of a nice turd, bed of woodchips or pasture and usually, several species of fungi coexist in the same spot. So sometimes a shroom (cubes, libs, cyans, whatever) will come out on top or perform good enough to fruit and sometimes they, well, don't. In that case, you don't find shrooms there. Pretty much explains why not every cow patty in TX is spawning lbs of cubes or copes when conditions are good.

The whole term 'contaminant' implies that there's one specific species that's intended to grow and the others (contaminants) are unwanted. Of course, that's not the way it works in nature. It's just a battle of survival out there.

Hope this helps.

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Great explanation. 

Here is a thread by RogerRabbit, which exemplifies the notion that "contamination" is subjective.

His Sparassis crispa project became contaminated with Psilocybe cubensis!
http://www.shroomery.org/forums/showflat.php/Number/5466797#Post5466797