Are they too good to carry cash? God, I hope William knows how to buy a carton of milk or treat the lads to a pub round.
Having been behind him in a shop and seen Catherine in a supermarket carpark I think its fair to say William and Catherine and their generation at least know how to shop for themselves.
I guess they have a totally different household structure - I find if people get rich, housework is the first thing they are ditching and "outsourcing". So Kate and William might not be alone in that situation. Having a housekeeper (who cleans, tidies and shops and cooks) is a rather common thing -my sister works in that area and earns a lot of money, because finding someone reliable does not seem to be that easy. She works (part-time) for a few people who are happy to have a life-out housekeeper who tidies and cleans for them (in bigger houses they even have more staff), shops and prepares a meal for night time.
A lot of them prefer never meeting her ... so I think that could be the reason why Will and Kate moved away from Kensington, to manage without a live-in housekeeper now.
I can imagine if you are in Buckingham Palace you are just part of a massive system - more like a play you have an assigned role, you can't be "human" there.