Exactly. In my area, houses in 'the city' are twice as expensive as comperable or larger places 30 min away. So, if more people move to the nice parts of the city to stay close to work, that's only going to make the housing prices there go up, and make it more economical to live outside the city.
This is new urbanist/smart growth propaganda. I'll believe it when I see it, this "flight" from the suburbs back into high density/high cost cities. I also love this prediction that light rail will save us all and that folks will FLOCK to high density condo developments on rail lines. It doesn't happen. It's a niche and that is all. Me, I'm looking to the exurbs of my city for better cost of housing, and much lower property taxes, thank you.
What happens then is that the not-so-nice parts of the city get gentrified and become nice parts. We've seen that happen in New York, Boston, and D.C. as the price differential grew large enough to take advantage of.