Are these models too skinny to be healthy?

These girls are without a doubt very unique, beautiful and hardworking, however when I saw Karlie Kloss (on the right) walk the VSFS this year I was shocked at how much skinnier she looked than any other VS model I have ever seen except for maybe Lindsay Ellingson (on the left) who is also super thin.
I'm not sure anyone can be that skinny naturally and today I read an interesting article which said...

"Twenty years ago the average fashion model weighed 8% less than the average woman. Today, she weighs 23% less."

"Most runway models meet the Body Mass Index physical criteria for Anorexia." (PLUS Model Magazine)

So what do you guys think of this? & btw Karlie is only 19 years old!