My early birthday party photos from the 80's show my parents friends in them,as do my husbands- and some of them had no kids, so I hardly think it's a new "trend". I remember some of the kids in the class having "over the top" parties, but most of us either had a party at home or at the local Mickey D's. I think that in general, I've seen the parents friends and any kids they might have get invited to kids parties until the kids get to be daycare/school-age and start having their own friends to invite.
I really don't see why one should get bent out of shape over an invite- I don't drink very much, but if somone invited me to a cocktail party I wouldn't get angry about it, I'd just decide if the company was worth the bother of dodging martini's all night. I'd rather have the choice of deciding for myself, than miss an evening of socializing with people I like because someone was worried the invite would offend me.