This is just anecdotal evidence, but I've also heard of firefighters have extreme difficulty defeating barred windows, etc. in attempting to perform rescues. Speaking as the son of a contractor I know there's a wide range of construction techniques. Some doors can be pulled out of the frame quite easily while others are very robust.
Isn't another problem with barred windows is it makes it harder for the people in the home to escape from a fire? Or do barred windows generally come with some type of emergency release for just such an occasion?