I don't think this is an American import, and I don't think this is a 'middle-class thing'.
I can remember similar events, can't remember what they were called, in Scotland in the early 1970s. It was family events, so my grandmother, mother, aunts, and their close female friends. One of my aunts would be the new mother. There was tea and cake and gossip, and gifts were hand-knitted matinee jackets and similar (my mother was a fantastic knitter). Or some bibs. Nothing big, nothing expensive, just a 'minding' - as a small personal gift was known then.
I think I would find a shower with a gift list very presumptuous. And yes, grabby.