I feel like you can probably do everything you want without claiming copyright on other user's content.
Facebook is somewhat similar in that people post content on Facebook and Facebook publishes it various forms. Here's what they say on their site:
Do I retain the copyright and other legal rights to material I upload to Facebook?
Yes, you retain the copyright to your content. When you upload your content, you grant us a license to use and display that content. For more information please visit our Statement of Rights and Responsibilities, which contain information about intellectual property, as well as your privileges and responsibilities as a Facebook user.
https://www.facebook.com/help/?faq=193430577370347#Do-I-retain-the-copyright-and-other-legal-rights-to-material-I-upload-to-Facebook?
I feel like saying you own the copyright reaches farther than you need to, and in doing so you're putting people who contribute to the forums in a position where they may be participating in illegal or dishonest activity (e.g., take a picture, post it here, and then printing it). Whereas, if you simply said "Posting content here gives me (Paul Wheaton) the license to use it in any way I want" is actually more amenable and still leaves the copyright in the hands of the creator.
Does this really matter all that much? No probably not. However, I think it may discourage some people from posting their full content on this site and instead link to it, and I think that would be disappointing and unnecessary.
All that to say: Thank you, Paul, for these forums and the wonderful podcasts, videos, and articles. I'm indebted to you for the information you've provided.