One of the things your comparison glosses over is the instances in which decisions made in the name of "accessibility" end up being more widely applicable. The

One of the things your comparison glosses over is the instances in which decisions made in the name of "accessibility" end up being more widely applicable. The classic example I see a lot is the idea of the wheel chair access ramp. Able people on bikes, anyone dragging a wheeled cart or bag, etc; they all get some tangible benefit from having ramp access. There's a certain danger in design spec to the "average" since any individual user is likely to have some diverse collection of needs and targeting what appears to be niche, can end up being much more representative than the "average" might suggest.