You'd think so, wouldn't you??
Apparently we've for the most part become so Westernised that we stay indoors most of the time, so the sun's there, we're just not taking it in.
I've also heard claims that Vit D takes time to absorb after exposure - that showering up to 24h (or 48?) after being in the sun reduces intake by a lot. Let's just say people aren't walking around soaking up sunrays and then not hitting the showers here.
But this is just stuff I've heard, I can't vouch for any of the claims.