Graveyard of the Fireflies was not targeted towards older viewers. In fact, it was released in theaters alongside with My Neighbor Totoro and both films target audience were children.
Moribito is also an anime adaptation of novels aimed at children.
The fact that both series you thought were aimed at adults were in fact aimed at children and their parents just corroborates once again how different American and Japanese culture are, I believe.

“Rather than call an increasing interest in children’s anime “regressing,” I’d call it expanding one’s interest and familiarity with Japanese animation. ”

I think it has more to do with the fact that it’s the last segment of the industry where they actually try to make the content appealing to a broader audience, rather than just otaku; so they actually bother working out decent stories more of the time.