Some interesting thoughts, thanks.
My OB said he was concerned about going past 42 weeks as the risk of stillbirth increased significantly. I had also heard this from midwives.
But, I also read something referencing a study that the average gestation for first-time mums was about 41+3 or something like that. (maybe it was the same study you refer to finsmum)

I wonder how much of this is psychological - when a baby is stillborn at 42 weeks, the natural reaction is to think "Well if we'd delivered earlier, this wouldn't have happened"...