Hi,
I would on the whole agree eexcept that many postural problems develop during adolescence. People who complain of chronic LBP often have their first episode in their teenage years - i think Peter O'Sullivan told me that but I don't remember a reference...
My point is that yes often people overcome the growth spurt tightness but in that time, what postural habits are forming? And it doesn't always have to be about short muscles. Girls that develop breasts earlier than their peers will round their shoulders to hide it. Often this posture carries over into adulthood, etc etc.
For what it is worth, I too don't stretch before exercise but i do get quite warm first. It really depends on what you are doing. For golf, i prefer to be not to be stretched at all because i lose "feel" and for squash, i prefer to be sweating before i can play at a hard level.
I think stretching for children is ok so long as it is done correctly and not over stretching. It might form a good habit for them later in life!