I think I’ve actually literally never since getting married asked my parents or in-laws for anything at all, whether goods or services (beyond “pass the potatoes” or “could you hold the baby while I pump?”). I grew up in a poorer WASP family and married into a better-off Catholic ethnic family. I was very, very, very proud as a newlywed, and I actually felt rather offended when my FIL sent us checks from time to time. But my attitude as changed a lot since then–I’m much more pragmatic than I used to be and less proud. For one thing, it’s not all about me and my feelings anymore–we have kids, and they need stuff. The time hasn’t come yet (and hopefully it will never come), but if my kids genuinely needed something, I would suck it up and have my husband ask my in-laws, and it would be the right thing to do.
It all depends on the actual situation and family dynamics, of course. I believe, for instance, that pensmama87’s husband is an only child and that his parents are reasonably well-off, so that enters into the calculation. Also, family cultures vary–in many families, it would be regarded as offensive or hurtful not to inform older family members about serious material needs. My in-laws would feel that way, and I can imagine feeling at least a little the same way down the road, when our children are grown and have families of their own.
You’re quite right that any help should be asked for, rather than demanded.