They are also painful when they are the edge of your lawn, the grass is kikuyu, and the time is spring.
Why should't the grass be allowed to snake its way over the concrete, slowly smothering the entire footpath?
Okay, yes, you're right - of course it can.
But not in my front yard - at least, not any more.
So maybe I'm the one who has the problem with edges! They're nice in principle.