Something that came up in a conversation offsite between me and Adelene Dawner:

Both in canon and MoR, where are all the grandparents and great-grandparents?

Supposedly, wizards have much longer lifespans than Muggles. I'm a Muggle, about to turn 22, and I've still got a grandparent left. Meanwhile, baby Harry managed to be orphaned without any of his grandparents stepping forward to take him in, or even trying to have a relationship with him. Perhaps Lily and Petunia's folks, Muggles both, were dead by this time - they never show up in canon - but what happened to pureblood James's mom and dad? Or their parents, or their siblings - when these people could all easily have lived to be a hundred years old, there should be some many-generation families running around.

The only visible ancestors we have before the canon epilogue are Augusta Longbottom, and, by the end of the series, Andromeda Tonks. Old characters like Dumbledore and McGonagall exist, but seem unmarried, childless, grandchildless. The Weasleys had at least one great-aunt and one great-uncle, but neither Molly nor Arthur has parents coming around for dinner, and they try to be an awfully close-knit family.