And the frame reinforcements for caliper mounts, the extra spokes, the disc compatible hubs, the thru axles, the heavier brake levers, and probably some stuff I'm missing.
No need to get emotional over this stuff, I love my hydraulic discs but they are heavier at comparable price points. It's also not particularly important to have a bike weigh a bit more, I was just letting the OC know that he was wrong on that aspect.