Why are there badges for meta on Stack Overflow? I understand the sites are intertwined but isn't it a little redundant to have badges for a site that already has a badge system in place?
Every meta site awards badges. It's just more noticeable on MSO since it looks and feels like a "regular" Q&A site.
The meta-related badges on the main sites, including Stack Overflow, are there to encourage meta participation. The fact that meta itself awards additional badges for participating on meta is somewhat irrelevant.
By and large, folks don't go looking for new sites to join just for the sake of earning more badges. (Although we have 100 sites now, so go nuts, y'all. :)) They start by getting interested in the subject and in the case of meta, the subject is site governance and moderation. If it takes a main-site badge to draw attention to meta and pique a bit of interest... sounds great to me.