Unfortunately, you are not representative of the average Facebook user. The average Facebook user is much less privacy savvy.
Not everyone uses Google (most do), and Gmail surprisingly isn't the most popular internet mail.
Facebook may not know as much about you, but they often know much more detailed information (ie, where you were last night).
Most of Facebook's users don't consider their "wall" to be public despite the fact that Facebook defaults it to be so (and has repeatedly reset privacy settings in the past to be "more public"). Complicate this with the fact that others can "implicate" you with their messages written on your wall. Despite you hiding them, they are there, in Facebook's servers just like your Google searches... except you didn't write them.
Unfortunately, you are not representative of the average Facebook user. The average Facebook user is much less privacy savvy.
Facebook doesn't know anything about anyone that they're not comfortable sharing with at least one other person. Google knows things about people they would never share with anyone. That's a fundamental difference, not related to privacy savvy.
Facebook does have lots of dirt people only want to share with a few people, however.
Facebook may not know as much about you, but they often know much more detailed information (ie, where you were last night).
Most of Facebook's users don't consider their "wall" to be public despite the fact that Facebook defaults it to be so (and has repeatedly reset privacy settings in the past to be "more public"). Complicate this with the fact that others can "implicate" you with their messages written on your wall. Despite you hiding them, they are there, in Facebook's servers just like your Google searches... except you didn't write them.