Doesn't the physical action of cleaning do a pretty good job of cleaning off yeast and mold? I would think that the cleaning is at least as important as the sanitizing. Also, even though starsan doesn't kill yeast and mold, doesn't the physical action of rinsing with the liquid knock the yeast and mold off? I have no idea if this is true but it sure seems like it would help.
Depends on your cleaning regimen. If you have a glass carboy that you scrub with a brush and then have a washer/rinser that sprays with a high velocity, you probably get most of it off (spores can be pretty hardy, though, if there is _anywhere_ for them to hide). Even in relatively hard plastic (like a better bottle or bucket), a soak in PBW/Oxiclean with a good carboy rinser and a microfiber towel will get you several good years of reliable use. I have a hard time with the concept of using a plastic fermenter for more than 5 or 6 years just due to wear and tear (less problem with a mash tun though).
In a pro brewery, they clean in place, and the biggest source of problems is going to be T or similar joint with 'dead ends'. Maybe there was a sensor or another vessel there at one point and they removed it and capped it. Now the CIP solution won't flow there, and it can now harbor all sorts of things. I wouldn't be surprised if the aforementioned pro brewery had a problem along those lines.