I was wondering if there is any caching done with these utilities.  I assume not, but not positive.  Are there any typical similar utilities that do use caching to speed up results on subsequent runs?
Does du or df perform caching?
files;filesystems;disk usage
There is no need for caching in df as df does a single statfs() call (per filesystem). And obviously this call does read files on disk and sum up their sizes... The filesystems (e.g. the kernel) keep track of the free space.du uses (without being aware of that) the page cache all applications use. In order to cache explicitly between runs there would have to be a du daemon anyway.