People seem to confuse a celebration event for a fund raiser. An invitation to a wedding is not synonomous with a demand of a gift, or at least it shouldn't be. I was taught that if there are specific things you need or want, it is appropriate to register accordingly and then let people like your family or maid of honor know where you are registered (or in leiu of being registered, what it is you need) in the event someone asks. The bride or groom may even be asked directly what they would like, in which case they are then free to make suggestions. Under no circumstance, however, should the bride or groom say, "You're invited to our wedding and, oh, by the way, this is what we want from you." This tactic, along with the current trend to inclose your places of registry or what you want for a gift in you wedding announcement or invitation, is the height of presumption and poor taste. And when the soon to be wed couple has already set up house, and are instead looking to fund real estate purchases or dream vacations, its just that much more distasteful.
The tradition of wedding gifts and showers was originally intended to help the new couple get their own household established. With the change in values over the past generation enabling couples to be established in their own household prior to being married, many have begun to treat gift giving as an entry fee to an event. Maybe someone should start a new tradition of giving Emily Post as an engagement gift to couples planning a wedding...