[gumby]

A couple of good examples of "good usability benefits everyone":

The company OXO makes kitchen gadgets originally designed for reduced mobility (i.e. older people) but now popular with everyone.

The ADA: having, for example, a ramp, doesn't just help people in wheelchairs: if I have something difficult to carry (or am using a cart) or have a temporary injury that makes steps hard to navigate I'm glad there's a ramp.

In many ways I consider the vast majority of designers and architects to be working away from their putative goals, instead pursuing egotism.