I'm the project manager for the remodel division of a large, privately held plumbing company in Houston. We run about 15 technicians just about 10 hours a day and I've seen some pretty crazy stuff. We don't run into too many homes that don't "have" a clean out. The problem is, most people don't realize that piece of PVC sticking out of the ground can be vitally important and they tend to cover them up with grass or even mulch.
I have two on my home. One I make sure stays uncovered. The other is 8' away from the house, 4' back from the front corner. My wife was trying to be nice one weekend and while I was working, decided to mow the yard. Well, you can figure out the rest of the story. Had to cut the top off and install a new cap and buried it.