Actually they DO grow fungus. The humidity in some central aircon system is actually not as low as we think. My office is >55%. I personally have seen lenses stored in funan growing fungus, but I am not talking about camera shops though, just camera enthuist.
Brand new lens sitting in airconed shops can grow fungus. This is especially true for lens that are not very popular and see very slow stock movement. For instance, when I searching for the sigma 150mm macro, out of the 3 copies that I looked at, 2 were showing signs of early fungus growth. It is only obvious when bright led light is used to view.