$170k split four (or more) ways actually doesn't sound like much, especially when you consider their location (NYC), and their massive student debt. NYU isn't a cheap school.
On a personal note, I lived in Harlem on a $24k/yr grad student salary this past year. It was a reasonably comfortable living, but being poor in New York City adds a lot of stresses to life that don't exist elsewhere. Walking around piles of dog shit and trash every day takes its toll after awhile.
I was actually surprised how well I made out, considering I was making the least amount of money I have ever made since age 19 and living in the most expensive city I have ever lived in my life. That being said I could be a lot more comfortable with just a slightly higher income.