My simple analogy:
I've watched my wife carry-around a 10 Lb sack of potatoes in the grocery store for over an hour w/o any though of THAT HEAVY WEIGHT! Offered to carry it for her and she said its OK its not that heavy.
While we're convinced that a similar weight (MINUS a potatoe or 2) just "kills us" on a similar hike!
Simple, your wife is tougher than me, I'd have gotten a cart.
