I know personally from my perspective I hope that my brother's wife will eventually be a daughter-in-law who actually proves her words correct. They are both calling my parents to move into their new house. And I hope this is for my parents to enjoy their golden years and retirement. But so far they decline the invitation because they want to retain their independance and separate lives. My parents don't want to be a burden and they don't expect anyone to cater to them. They also have a secret fear that their kids (including daughter in law) will not act as a safety net when they need it. I think most of the expectation is placed on the eldest son to take care of parents.
My s-i-l was 19 when she married so she was not very 'trained' in terms of domestic responsibilites. There were many occasions when my mother was the only one in the kitchen doing tons of cooking and dishwashing for dinner parties, get togethers etc. My mother never said anything to her. It's not like a major expectation to have a d-i-l who will just swoop in and do all this work, but it would show that she cares. I think that's the major issue. If a d-i-l wants to show her respect and love then she will not let her m-i-l work too much.