A guy once drove me more than 50 miles to a restaurant from Dallas. People tend to travel long distances there...so it probably got a lot of the city business.
The metroplex is seamless. You can drive from Dallas, through Garland, on through Richardson, and up into Plano without ever crossing an undeveloped block of land. The term suburb is actually pretty questionable when you look at it like that. The metroplex is really just one huge city.