Bachelors. Not as in Bachelors degree, but literally bachelors: They're young, cheap, work crazy hours, and easily seduced by free pizza - the ideal startup employee.
Can agree. I used to be like this and loved the free pizza. Now I'm earning more working my slightly less shiny corporate job with sensible hours. I have time to cook decent pizza though!
This is what I assumed. They're biased towards younger programmers with no life circumstances that would cause them to need a higher salary (e.g., kids).