in reply to [SOLVED] Why do some modules not get tested
The above answers are probably what you are looking for but I just thought I'd let you know of a few more.
Some modules don't receive smoke reports from automated smokers because they are black listed. I'm not smoking right now but I had a list of black listed modules for various reasons - tests took way too long, downloaded loads of stuff, prompted without using prompt etc
Some automated testers abort a test if it takes longer than some time - assuming the test has hung.