I am not sure on this one. I know we all would rather have the money - so that we can start off right- to help with a down-payment on a house or to help with the honeymoon. I think I would be offended if on the invitation it stated- no gifts- money please.
I was invited to 1 that asked for gift cards to a lumber yard- they were rebuilding their house. I had no problem with this- as it was a suggestion.
Demanding money or any specific items were never a good idea to me even from close relatives unless they make an offer to you on the things that you want. I know it is your big events but we do have to keep in minds we have no rights to it at all.