I also don't get the issue with asking for money. If you don't need anything else, and the money would really help you out or give you something to enjoy yourselves with, then absolutely tell me and I'll get what you want.
Rather that than waste money on things that aren't wanted/needed, however nice they are.
We asked for money for our wedding, but we appreciated absolutely everything of course. And we really didn't mind whether people got us nothing, a small amount or a larger amount of money, if cash was their way forward.
We asked for money, we didn't demand it, and I certainly wouldn't have wanted anyone feeling like they had to turn down the invite for the sake of not wanting to give a gift. They were the important bit, not the money.
As it was we were given cash that allowed us to go on our first ever holiday together. Some people gave lovely little gifts and decorations, instead. We did get a lot of photo frames, and we've never been able to use them so they're in a drawer half a decade later. One person gave us a £1 bag of sweets. We loved that. It was great after the stress of the wedding (because getting married might be fun, but it is hard!) to get home the next morning and just sit and share a bag of sweets whilst we relaxed. And of the guests that gave us cash, some gave £5 and some gave £50 and we really appreciated almost every gift equally.
The one gift that we felt a bit upset by was a £5 note given by a family of five that we'd invited. And it wasn't that it was £5. If they'd given that peacefully, we'd not have been bothered. But this family was a well-off family that seized every opportunity on their wedding day to brag about how much money they had. They compared the price of our wedding with ours and kept talking about it. They talked about how they were redecorating an entire room to match one small object within it, because they liked the object but couldn't possibly have anything out of place. The entire day was 'look how much money they have', and with all that the £5 felt like an insult.
But would a £5 note be an insult otherwise? Not at all. It's a lovely gift and would pay for a dessert at a restaurant if we went out, or a DVD and popcorn for a night in our holiday accommodation. Every £1 made a difference, and every gift (money or otherwise) was appreciated.
The only reason for the money request was to stop people spending their hard-earned money on (much appreciated) gifts that we wouldn't ever be able to use. And some ignored our request, as was their choice.