Correct me if I am wrong, but adding terms to the query can have two distinct effects:

Either this would add jobs that hit "software" or "developer" in isolation,(see original problem) or it would filter out "Embedded programmer" or "Embedded systems engineer", if those ads didn't include all three individual terms "embedded", "software", and "developer". (Why I tolerate my current approach)

I've always assumed I was casting the optimally sized net with a single keyword, and no better alternative existed for purposes of completeness.