I remember my mum saying to me when I was in my mid-20s that if I ever had a baby, she'd look after it. This was purely hypothetical at that stage as I hadn't even got together with my now DH and babies were certainly not on my radar. It might have come up in a conversation about her not liking the thought of very young children being in full-time nursery. So in a way I expected some help, but if she'd said at the time, "Just so you know, if you ever have a baby, I'll babysit occasionally but that'll be it," then I would not have done.
Fast-forward a few years and DH was absolutely adamant we had to live near my family (his parents are dead) when we had children. Obviously he hadn't read any threads like these! My parents don't do any formal childcare in the sense that they don't have them every Tuesday, for example. But my mum sometimes comes round and minds the children (oldest is at school) for an hour or two while I do some work from home (I do freelance proofreading) or get on with other jobs. She also used to help with cleaning (at her insistence, I hasten to add - I didn't ask her to) but doesn't so much now as she had an operation on her back last year and I have more time now DD is at playgroup some of the time. She also feeds our pets when we are on holiday and probably babysits around 3 evenings a year (which is not too strenuous as DCs will hopefully be asleep). My dad tends to come over once a week for a few hours. He does childcare in the sense that he plays with DD while I get on with jobs around the house and has occasionally babysat. My mum still has plenty of time for holidays, meeting up with friends, Ramblers walks, history talks and volunteering.
Locally, I would say the majority of parents I know have at least one set of GPs nearby, although not do childcare. There are always lots of GPs on the school run and at toddler groups. Some say their children would not be able to afford childcare otherwise. One I met was also looking after her 95-year-old mother.
My mum had less help than I've had, because neither set of parents was nearby. However, they came to stay when, for example, she had my younger sister, and later on when she went on week-long residential courses or was ill.
DH's sister obviously hasn't had any parental help, but her husband's parents will have the kids overnight from time to time or for a few days when they go away, and they used to go skiing with them so they could mind the grandchildren while the parents skied. My mum had one friend who died recently but who had moved house a couple of times to provide childcare for her doctor daughter (she offered to do this).