"(pads might be) unnecessary as long as we use materials that are sufficiently conformable to the shoulders while being sufficiently inflexible"
Mark brings up a good point; in fact, with my loads typically under 15lbs, I'm probably a prime candidate for padless straps. But a funny think happened on the way to the Forum, so let me share why I think pads are still a great feature:
I used to attach the top of my straps to my pack with belt (along with some backing). On one occasion, I reasoned that I could simply sew the 1.9 sleeve to the 1.9 pack, and skip the belt on the top. After I penciled it out, I realized all I had to do was add an extra 2" or so to the sleeve and I'd be good to go.
OK, so here's what happened: after I sewed the sleeves to the pack and placed my folded sleeping pad inside along with other items, I jimmied and jammed my (3/8" neoprene) pads - I hadn't yet secured them with a cross stitch - up to the seams so tight they almost stuck out perpendicular to the pack before finally yielding to gravity and sort of hung down.
Why is this important? Because once I finished the pad buckles and got the pack on, I realized I had created a very rigid strap system. I got excited and quickly finished my hip belts using the same exact method. (Of course, once buckled up, both padding & fabric easily bend & conform.)
Well, you can guess what this little baby felt like - heaven! No stays, no compression straps (my pack is carefully measured so the bear can fits snug), yet there it was, barely any sway in a completely frameless pack weighing under 8oz.
So, yeah, in my particular case, the addition of a few ounces of padding actually turned out to be a key part of the frameless aspect, rather than just to offset weight on my shoulders & hips.