boy you said it, especially after seeing the facebook page of them weighing their bikes. Assuming her bike weighs in the 35-40lb range, lets assume 40, if her total bike with stuff weighs 110 or whatever, thats 70lbs of gear!
I have mentioned numerous times on this forum how when I biked in the Gaspe region way back in I think 1990, I had too much stuff and it just wasnt fun on the steep stuff (and just damn heavy in general). I learned reeeeally quickly that I never wanted to repeat that, and certainly took a good 10lbs off or more for the next trip.
I really cant imagine lugging 70, 80 or more lbs of stuff, not for me in any case and my legs. As you say, I too can admire (or rather marvel) how some people can physically do that, but I think its fair to say that first timers will often make the error of taking too much stuff, from inexperience not really choice, and adjust afterwards (or during a trip).

when I spent some time in Costa Rica this May, I had about 25lbs of stuff I think, rear panniers and handlebar bag only, and even that amount was so much more fun going down curvy mountainous downhills than fully loaded. The bike handled really well and this touches on what a number of you have touched on, the fun factor or riding-how the bike feels when lightly loaded, and I completely agree with all of you on this point.
There is a real joyfullness in riding a bike that isnt truck-like, and while I havent toured as light as you guys have, I really do see the appeal simply from the "tossability" angle--and especially so if on dirt trails or anywhere where you have to be making directional changes a lot and/or using body english to move around stuff etc. (not to mention as Asana said, about carrying ones bike over stiff etc etc)

a final note-one of the numerous reasons I tend to always migrate to the touring section is how the postings and tone here are usually well thought out, informative and especially respectful . I put the last point up there as the strong point of this joint and hope that this doesnt change.