I think the point might be that doors can pop open and it's the PIC's job to notice it, in spite of completing a checklist. I own a twin Piper and it's pretty easy to think the door is locked when it isn't.

Complaining about DE's is nothing more than rationalizing a failure to make yourself feel better. If you do this at an interview, blame the DE for busting you and not take ownership of the failure, it doesn't put you in a good light.