Ask HN: Why is "public" the new default setting for user profiles?

I just signed up for a Grooveshark account and was given a vanity url which I guessed was public. Pasting the url into another browser confirmed the hunch. I then had to search for settings to make my playlists and history private. After setting these, I was still able to see personal data. Why would they do this? I've deleted my Facebook account over privacy concerns but now it seems like many sites are following suit with more and more public data. I don't presume all my online activity is private, but I would prefer if it weren't wide-open by default.