I've never attended one, but my first reaction to your post was that it was all about the "gimme" a gift then get out because the host doesn't want to have to spend the $$ or time to plan something.
If it were more like an open house, even like a happy hour cocktail party where only hors d'oeuvres are served and drinks, you visit with the bride a bit and open the gift together, then you go or mingle if you like - then I can see that.
But I think it's really tacky to invite someone to bring you a gift, they have spent their time and hard earned money and probably gave the gift some thought and nice wrapping, then not even offering a bite to eat or drink as you stay and mingle - super tacky.
However, if I didn't know or much like the person - then, yea, get me the hell outta there - I wouldn't care less :)