It's not 3 minutes, it's 3 minutes after they're so emotionally worked up they're crying. Finding out that your parents heard you but just ignored you is going to make you trust them less. (How do you define "emotionally healthy"? I grew up in a really nice home but my brother and I still have some problems.)
Do you have children? Children cry as an expression of many things, because they can't express themselves in other ways yet. You make it sound like once children get to a state of crying, they must have endured a lot already, which is not true. Allowing children to cry for several minutes at a time before going to check up on them is a pedagogically sound and normal technique for teaching children to go to sleep by themselves, for example.
(two girls) Being upset in your familiar comfortable bed is a very different thing than accidentally trapping yourself in a tiny strange dark box and physically struggling to get out. Very different chemical things happening in your brain in those two situations.
Sure, I'm not saying parents have to come running every time or anything. The point is that letting a kid cry until he goes back to sleep is consistent. Locking your kid in a box to see what happens is not. How will the kid know next time he gets stuck, that it's not just another test? And since the kids are still learning how to communicate, adding a continuing doubt that maybe their parents understand them fine but have chosen to ignore them isn't going to help.
