I must admit we have a divide like that too. My wife will stir at the slightest noise, whereas I assume that a murmer or two is just a random noise and safe to ignore.

Obviously if the baby is crying heartily either of us will investigate, but I don't feel the need (most of the time) to check on him if there are sporadic gurgles, laughs, or "noise".

That said I think my wife is coming round, she's started sleeping with earplugs now so that she doesn't wake up unless there is a real "emergency".