My expedition tourer will take me to the end of the world and back. It is a steel custom bike with 26 inch wheels, a Rohloff hub, drop bar, Magura HS 66 hydraulic rim brakes, and a SON hub generator and lights. For a Rohloff shifter for drop bars, see: http://www.mittelmeyer.de/ The bike is built for strength and reliability, so I think the 16 kg all in weight (including a frame lock, rear rack, fenders etc) is not bad at all. The Rohloff hub is perfect for such a bike for rough conditions.
Of course, a lighter bike would be nice, but compromises would be necessary. I will not use dangerous parts like carbon rims, handlebars or forks, and my bike needs to cope with pretty severe off road beatings and unsympathetic bagage handlers. The light end of the sensible range would be a 10-12 kg (complete with fenders, racks and lights) classic 650 B rando bike in the French tradition. With one of those you could still take ultralight camping gear in a French style bar bag and a UK style saddle bag, and with 38-42 mm tyres you could comfortably and safely ride not only tarmac, but also fire roads and most trails. I am comtemplating getting one built, as an alternative to my loaded tourer, for lighter and faster but less demanding trips.
I have been reducing my luggage weight considerably over the last few years, but cycling will always remain a bit different from backpacking. Ortlieb are currently experimenting with (and selling small numbers of) considerably lighter pannier bags, but even so, those still need stiffeners and relatively heavy mounting systems. Cyclists also need tools and spares to the tune of at least a pound, and sometimes two pounds. On the other hand, weight is not nearly as critical as it is with backpacking. On flat terrain weight matters little. But with climbing it sure does.