Dissecting "He Didn't Have to Be" by Brad Paisley

Brad Paisley applies his self-consciously retro schtick to the concept of grace in a modern family, in his late-1999 breakthrough hit, "He Didn't Have to Be". But what exactly is the nature of his throwback vibe? What's surprising about it, and what about his neo-traditionalist-influenced vocals works so well with this song's whimsical melody?  "When a single mom goes out on a date with..."