I don't think anyone is asserting that gas prices alone will cause people to move. Over the next 20 years or so, many people will have to move anyway, whether they're getting a new job, moving out of their parent's house, moving from an apartment to a house to have kids, or retiring to a smaller house, or any number of other reasons. For these people gas prices and neighborhood walkability might be a significant consideration in where they choose to live compared to people who moved 10 years ago, especially if they were previously living in the suburbs and have felt all the ill effects of it.