I'm no longer there, but I grew up there, and I would say yes to an extent. Yes in that there's a large amount of movement within the area (e.g., grow up in Dallas, go to school at A&M, settle in San Antonio) and that you may have to go to one of the other cities now and then for something specialized (e.g., from Austin to Houston for a consulate or a highly specialized medical visit). There's also somewhat of a rivalry, I guess. But, still, there's not a "feeling" of connectedness, but is there between, say, Baltimore and Philadelphia?

I can't really compare it to the Northeast Corridor, though. I lived in NYC, but not long enough to really have a connection much beyond the city.