Prairie Stash
IMO, it is gross to ask for specific gifts from your friends and family, that you have no intention of keeping at the time that you ask for them, but intend from the start to return for cash. Especially so, if you ask for $100 items simply because they are easier to return (plate set you don't even like) than a bulky item (vase / comforter).
The people who attached the gift receipt did so in case you get a second / identical one, or they buy queen size bedding and you need a king size, or they buy purple but your kitchen is orange, etc.. They actually want you to use the gift and not return it, but if you can't use it, they would rather you exchange it for something that you can use.
If they wanted to give you cash or a gift certificate, they certainly would have, for the wedding or otherwise, as buying a gift takes thought and care and time. In the case of your grandmother, she would have given you cash in advance of the wedding, for example, or as an amount to "help set up your new home / buy yourself dinner on moving day" and then provided a simple present for the wedding itself, if she actually wanted you to have money, but thought it bad luck on the day of.. Grandma's are kinda cool at that.
If your culture dictates no cash as presents for weddings, then accept and use what you get, or exchange the gifts for something you can use (not just return for cash unless there is no option such as at a small boutique store).