I love this question!
I actually did a bunch of research in this area and presented on this topic to the undergraduate exercise science students at USF. I am also a living example of this (I do not do any crunches/abdominal exercises). Abdominal exercises are not required to tone your midsection. Most individuals have developed a rectus abdominis from daily activities, however they are merely covered with fat. Not to mention abdominal can only hypertrophy minimally as compared to other muscle structures. If your goal get a “six pack” or create a healthy core/mid section I would focus on isometrically contracting your core musculature during exercises. For other information regarding core/back/abdominals look into Dr. Stuart McGill’s research.
Fuel the Movement,