The multiple shower phenomenon is trying to become commonplace here, but generally is not well-received. Outside of special circumstances, I find it ridiculous personally.
That said, it doesn't mean I think only a first should be celebrated. If I send a card, visit w/ a gift and sometimes even provide a meal or two, is that not an okay way to celebrate a new little one, or must it be a shower? If it must be a shower, don't expect a welcome baby gift also.
IMO I think a lot of this excess is driven by the same phenomenon where women are focused on the ultimate princess bridal experience and can't let that go once their day in the sun is over. I want to come to your wedding & celebrate the start of your marriage. Not so fun when what you really want is for people to spend the evening admiring your flowers, theme, decor, obscenely expensive dress, etc., etc., etc. I want to spend the evening in good company, celebrating your wonderful, happy future.