I suspect that those numbers don't tell enough of the story. The range of salaries in SV is huge. Netflix routinely pays more than 200k. Tiny startups pay < 100k. I don't imagine you see such a variance in DC. 50th percentile might only be 10k apart but I suspect the gap widens as you get deeper into the "above average space".

I do think that a developer getting paid 300k (not unheard of for top talent at top companies) in a place like Austin would be ridiculous.