This is an astute observation. Additionally, Apple just opened a large campus in Austin, which is also home to Dell. It's a good roll out strategy: middle of nowhere, semi-large city, then bay area/chicago and maybe even NYC.
If it were ever to be declared a CSA with San Antonio, they'd be of similar size to Seattle-Tacoma or Minneapolis-St Paul. Which seem 'semi-large' to me, especially on global scene.