The southeast has three major tech hubs: the Dulles corridor in NoVA, the Triangle in NC, and Atlanta. They also have quite a few good schools with big graduate programs that feed into the market (VT/UMD, Duke/UNC/NCSU, GT/Emory). The software work in these places is often some integral component of a meat-space product, and that meat-space product is often in a complex problem domain in which the specialization of a PhD is valuable. For example, if you're developing software for a UAV, it's valuable to have someone with domain experience in control theory. The specialized domains in D.C. are often defense related, in the Triangle it's often bio-related although quite diverse, and in Atlanta it's often logistics-related.
Certainly, Silicon Valley has tons of these sorts of jobs too. Google is full of PhDs. But the ratio of specialized domain products to consumer products seems to be higher in the southeast. And as a result, my perception is that the market's valuation of PhDs is higher. It's quite common to see companies in that market where not having a PhD is considered a severe liability.