Agreed, do we have any documentation on this? (I know the lobby industry conveniently has little documentation in general, but I'd love to see any papers written on the subject)
That Wikipedia article doesn't make that claim, and normalized by GDP actually contradicts it by pointing out that 5 of the top 10 of those cities actually have well-developed rail (I'd add DC and Atlanta to that list, bringing us up to 7 --- in other words, leaving out only LA, Houston, and Dallas).
I disagree about Atlanta. Atlanta does not have a well-developed rail. I should know - I live there. :)