You're comparing the weight of a mirrorless camera plus small image circle lens with a FF image circle lens? Well, then...the S100 weighs less than 7 oz./200g including the battery and memory card, and has a 24mm-equivalent f/2 lens. That comparison is only slightly less relevant, but if you want to save weight, there you go...
I prefer APS-C and DX cameras to FF. I don't sell 40x60 prints, I just shoot ads. If I need a really big print, than I'll use my 4x5 Toyo. My Only FF cameras are Full Frame Film
cameras. I like small light weight cameras and I'm getting a Sony NEX 7 with a Zeiss 24mm f1.8 to test. If the NEX 7 works out, most of my Canon gear goes into storage.
BTW if Canon builds a Pro Quality Mirrorless with the requisite small/light lenses, I'll get one to test.