I think children should not be in strollers past 5 years old unless they have a medical condition.
Seriously kids can walk better than adults at times.
I find parents will spend the whole day at parks with younger children and just stick them in strollers when they are tired, what's the point of that? If they are tired they need a break, there is so much stimulus at the parks, if they are tired a stroller is not the answer.
While a stroller may not be the answer for YOUR family, it may be the answer for someone else's family. Some children may need a break from the parks entirely, while other children are fine taking their "break" in a stroller.