I don't think its rude of a bride & groom to assume that those attending their wedding will be giving a gift of some sort. And I don't know anybody who would attend a wedding without a gift. In the same way, I have lots of wine and beer in the house, but if friends come over for dinner they still bring some with them. I do assume that they'll bring something, and would be a bit miffed if they turned up empty handed, because I'd find it rude. I suppose its the same principal really, assuming people will gift, but not expecting etc.
I also agree that it should make no difference whatsoever whether a couple would prefer money to have the honeymoon of a lifetime or a casserole dish. A gift is unconditional, and I would always prefer to gift something that will be valued by the recipient, for whatever reason.
For our own wedding we didn't specify anything, except to a couple of people who asked that we would prefer not to receive vouchers, other than that not bothered. We tend to shop in small independent shops, and I'm not overly keen on the typical voucher shops. As it went, most people put cash or a cheque in a card. A few people gave gifts. We already had everything we needed for the house, and have our own taste, so I wouldn't really want lots of household items that I perhaps wouldn't have chosen myself. However, the few bits we did get were mostly lovely, and we treasure them. One guest did get us a rather expensive ornament that has lived in its box for the couple of years since we married.
All in all, we received several thousand pounds, of which a fairly large proportion was spent on honeymoon - we went for dinner in a Michelin starred restaurant, hired a better car, upgraded our flights etc.
So I suppose after that long post, I think requests of any sort are generally unnecessary as when in doubt the vast majority will give money anyway.