I was part of a study at the university hospital where my shoulders were examined by ultrasound. They found both my rotator cuff muscles were torn (right and left arms). I didn't have any idea. How come I didn't have pain or something?

You didn't mention your age, your activity level, or any other health problems you may have. For example the rotator cuff does tend to degenerate as we age -- and sometimes without us even knowing it! This is because our activity level is starting to slow down too. We aren't doing those one-arm push-ups anymore that would signal a problem.

Arthritis often catches up with us and any new ache or pain is attributed to that. Many people get along with partial range of motion and strength just fine -- again, for the same reasons mentioned here. We do less as we get older so we don't notice a big difference.

It sounds like you had partial rotator cuff tears if you had no symptoms (or very few). With few overhead or contact sports activities, you could very well have partial tears and not know it.